Supplemental Prospectus - Form 424B3

Filed Pursuant to Rule 424(b)(3)

Registration No. 333-236100

PROSPECTUS

DELCATH SYSTEMS, INC.

2,762,657 Shares of Common Stock

This prospectus relates to the re-sale by the selling stockholders identified in this prospectus (each a "Selling Stockholder" and, collectively, the "Selling Stockholders") of up to an aggregate of 2,762,657 shares of common stock, $0.01 par value per share (the "Common Stock"), of Delcath Systems, Inc., a Delaware corporation ("Delcath" or the "Company") issuable upon (i) the conversion of the Series E Convertible Preferred Stock and Series E-1 Convertible Preferred Stock and (ii) exercise of Series E Warrants and the Series E-1 Warrants previously registered on the Registration Statement on (a) Form S-1 (file No. 333-236100) that was originally declared effective by the Securities and Exchange Commission ("SEC") on May 5, 2020 (this "Registration Statement"), (b) Form S-1 (file No. 333-235751) that was originally declared effective by the SEC on January 7, 2020 (the "2020 Registration Statement"), and (c) Form S-1 (file No. 333-233396) that was originally declared effective by the SEC on November 7, 2019 (collectively with this Registration Statement and the 2020 Registration Statement, the "Registration Statements").

The Common Stock offered by this prospectus (the "Registered Shares") may be sold by the Selling Stockholders or their transferees, pledgees, donees or assigns or other successors-in-interest that receive any of the shares offered by this prospectus as a gift, distribution, or other non-sale related transfer. For additional information on the possible methods of sale that may be used by the Selling Stockholders, you should refer to the section of this prospectus entitled "Plan of Distribution."

We are registering shares that are issuable to the Selling Stockholders upon the conversion of the Series E Convertible Preferred Stock and Series E-1 Convertible Preferred Stock and the shares of Common Stock issuable upon the exercise of the Series E Warrants and the Series E-1 Warrants (such Series E Warrants and Series E-1 Warrants, the "Warrants").

All net proceeds from the sale of the shares of Common Stock covered by this prospectus will go to the Selling Stockholders. We will receive none of the proceeds from the sale of the shares of Common Stock covered by this prospectus by the Selling Stockholders. We may receive proceeds upon the exercise of outstanding Warrants for shares of Common Stock covered by this prospectus if the Warrants are exercised for cash. We will bear all expenses of registration incurred in connection with this offering, but all selling and other expenses incurred by the Selling Stockholders will be borne by them.

Our Common Stock is traded on The Nasdaq Capital Market under the symbol "DCTH." On September 24, 2024, the closing price for our Common Stock, as reported on The Nasdaq Capital Market, was $8.94 per share. As of August 31, 2024, 28,000,843 shares of Common Stock were issued and outstanding.

The Selling Stockholders may be deemed "underwriters" within the meaning of the Securities Act of 1933, as amended, in connection with the resale of the Registered Shares.

This offering will terminate on the earlier of (i) the date when all of the Registered Shares have been sold pursuant to this prospectus or Rule 144 under the Securities Act, and (ii) the date that all of the securities may be sold pursuant to Rule 144 without volume or manner-of-sale restrictions, unless we terminate it earlier.

Investing in our common stock involves risks that are described in the section titled "Risk Factors" beginning on page 2 of this prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of the securities to be sold under this prospectus or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is September 25, 2024.

TABLE OF CONTENTS

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ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that we filed with the SEC using a "shelf" registration process. By using a shelf registration statement, the Selling Stockholders named in this prospectus may, from time to time, sell the securities described in this prospectus from time to time in one or more offerings as described in this prospectus. To the extent necessary, each time that the Selling Stockholders offer and sell securities, we or the Selling Stockholders may provide a prospectus supplement to this prospectus that contains specific information about the securities being offered and sold and the specific terms of that offering. To the extent permitted by law, we may also authorize one or more free writing prospectuses that may contain material information relating to these offerings. Such prospectus supplement or free writing prospectus may also add, update or change information contained in this prospectus with respect to that offering. If there is any inconsistency between the information in this prospectus and the applicable prospectus supplement or free writing prospectus, you should rely on the prospectus supplement or free writing prospectus, as applicable. Before purchasing any securities, you should carefully read this prospectus and any applicable prospectus supplement and free writing prospectuses, together with the additional information described in the section titled "Where You Can Find More Information; Incorporation by Reference."

Neither we nor the Selling Stockholders have authorized anyone to provide you with any information or to make any representations other than those contained in this prospectus, any applicable prospectus supplement or any free writing prospectuses prepared by or on behalf of us or to which we have referred you. Neither we nor the Selling Stockholders take any responsibility for, nor provide any assurance as to the reliability of, any other information that others may give you. Neither we nor the Selling Stockholders will make an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus and the applicable prospectus supplement to this prospectus is accurate only as of the date on its respective cover, that the information appearing in any applicable free writing prospectus is accurate only as of the date of that free writing prospectus, and that any information incorporated by reference herein is accurate only as of the date of the incorporated document, unless we indicate otherwise. Our business, financial condition, results of operations and prospects may have changed since those dates.

This prospectus incorporates by reference, and any prospectus supplement or free writing prospectus may contain and incorporate by reference, market data and industry statistics and forecasts that are based on independent industry publications and other publicly available information. Although we believe these sources are reliable, neither we nor the Selling Stockholders guarantee the accuracy or completeness of this information and neither we nor the Selling Stockholders have independently verified this information. In addition, the market and industry data and forecasts that may be included or incorporated by reference in this prospectus, any prospectus supplement or any applicable free writing prospectus may involve estimates, assumptions and other risks and uncertainties and are subject to change based on various factors, including those discussed in the section titled "Risk Factors" contained in this prospectus, any applicable prospectus supplement and any applicable free writing prospectus, and under similar headings in other documents that are incorporated by reference in this prospectus. Accordingly, investors should not place undue reliance on this information.

Unless the context otherwise indicates, references in this prospectus to, "Delcath," "the Company," "we," "our," or "us" mean Delcath Systems, Inc. and its wholly owned subsidiaries. The term "Selling Stockholders" refers, collectively, to the selling stockholders named under the heading "Selling Stockholders" in this prospectus and, as applicable, any donees, pledgees, assignees, transferees or other successors-in-interest selling the shares offered by this prospectus received after the date of this prospectus from the Selling Stockholders as a gift, pledge, or other non-sale related transfer.

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RISK FACTORS

Investing in our Common Stock involves a high degree of risk. Before deciding whether to invest in our Common Stock, you should consider carefully the risks and uncertainties discussed in this section and under the sections titled Risk Factors contained in our most recent Annual Report on Form 10-K and in our subsequent Quarterly Reports on Form 10-Q for the quarterly periods ended subsequent to our filing of such Annual Report on Form 10-K, as well as any amendments or updates to our risk factors reflected in subsequent filings with the SEC, which are incorporated by reference into this prospectus, together with other information in this prospectus, the documents incorporated by reference, any prospectus supplement and any free writing prospectus that we may authorize. These risks and uncertainties are not the only risks and uncertainties we face. Additional risks and uncertainties not presently known to us, or that we currently view as immaterial, may also impair our business. If any of the risks or uncertainties described in our SEC filings or any additional risks and uncertainties actually occur, our business, financial condition, results of operations and cash flow could be materially and adversely affected. In that case, the trading price of our Common Stock could decline and you might lose all or part of your investment. Please also read carefully the section titled "Cautionary Note Regarding Forward-Looking Statements."

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CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus, and the documents incorporated by reference herein, contain, or will contain, "forward-looking statements" within the meaning of Section 27A of the Securities Act and Section 21E of the Exchange Act of 1934, as amended (the "Exchange Act"). Forward-looking statements can be identified by words such as "intends," "believes," "anticipates," "indicates," "plans," "expects," "suggests," "may," "would," "should," "potential," "designed to," "will," "ongoing," "estimate," "forecast," "predict," "could," and similar references, although not all forward-looking statements contain these words. Forward-looking statements are neither historical facts nor assurances of future performance. These statements are based only on our current beliefs, expectations and assumptions regarding the future of our business, future plans and strategies, projections, anticipated events and trends, the economy and other future conditions. Because forward-looking statements relate to the future, they are subject to inherent uncertainties, risks and changes in circumstances that are difficult to predict and many of which are outside of our control. Risks that could cause actual results to vary from expected results expressed in our forward-looking statements include, but are not limited to:

Forward-looking statements speak only as of the date the statements are made. Except as required under the federal securities laws and rules and regulations of the SEC, we undertake no obligation to update or revise forward-looking statements to reflect actual results, changes in assumptions or changes in other factors affecting forward-looking information. We caution you not to unduly rely on the forward-looking statements when evaluating the information presented herein.

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USE OF PROCEEDS

We are not selling any of the shares of Common Stock being offered by this prospectus and will receive no proceeds from the sale of the shares by the Selling Stockholders. All of the proceeds from the sale of Common Stock offered by this prospectus will go to the Selling Stockholders at the time they offer and sell such shares. The Selling Stockholders will pay any underwriting fees, discounts, selling commissions, stock transfer taxes and certain legal expenses incurred by such Selling Stockholders in disposing of their shares of Common Stock, and we will bear all other costs, fees and expenses incurred in effecting the registration of such shares covered by this prospectus and any applicable prospectus supplement, including, without limitation, all registration and filing fees, Nasdaq listing fees, if applicable, and fees and expenses of our counsel and our independent registered public accountants.

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SELLING STOCKHOLDERS

The Common Stock being offered by the Selling Stockholders are those previously issued or issuable to the Selling Stockholders upon the conversion of Series E Convertible Preferred Stock and Series E-1 Convertible Preferred Stock, and those issuable to the Selling Stockholders upon exercise of Warrants. We are registering the securities in order to permit the Selling Stockholders to offer the Registered Shares for resale from time to time.

The table below lists (a) the names of the Selling Stockholders whose shares are being offered by this prospectus, (b) information regarding the beneficial ownership of shares of Common Stock by each of the Selling Stockholders, including the number of shares of Common Stock beneficially owned by each Selling Stockholder based on its ownership of the shares of Series E Convertible Preferred Stock, Series E-1 Convertible Preferred Stock, Series E Warrants and Series E-1 Warrants as of August 31, 2024, assuming the conversion of the shares of Series E Convertible Preferred Stock and Series E-1 Convertible Preferred Stock and the exercise of the Series E Warrants and Series E-1 Warrants held by the Selling Stockholders on that date, without regard to any limitations on exercises; and (c) the amount and (if one percent or more) the percentage of the class to be owned by such security holder after completion of the offering.

In accordance with the terms of a Registration Rights Agreement between the Company and the Selling Stockholders, this prospectus generally covers the resale of the sum of (i) the number of shares of Common Stock issued or issuable to the Selling Stockholders upon the conversion in full of the Series E Convertible Preferred Stock and Series E-1 Convertible Preferred Stock (subject to adjustment for reverse and forward stock splits, recapitalizations and similar transactions) and (ii) the maximum number of shares of Common Stock issuable upon exercise of the Warrants (subject to adjustment for reverse and forward stock splits, recapitalizations and similar transactions following the date of the Securities Purchase Agreements), determined as if the outstanding Warrants were exercised in full as of the trading day immediately preceding the date this Registration Statement was initially filed with the Commission, each as of the trading day immediately preceding the applicable date of determination and all subject to adjustment as provided in the registration right agreement, without regard to any limitations on the exercise of the Warrants. The fourth column assumes the sale of all of the shares offered by the Selling Stockholders pursuant to this prospectus.

Under the terms of the Warrants, a Selling Stockholder may not exercise the Warrants to the extent such exercise would cause such Selling Stockholder, together with its affiliates and attribution parties, to beneficially own a number of shares of Common Stock which would exceed 4.99% (or, upon written election by a Holder which is delivered to the Company prior to the issuance of any shares of Series E Convertible Preferred Stock and Series E-1 Convertible Preferred Stock to such Holder, 9.99%) of the Company's then outstanding Common Stock following such exercise, excluding for purposes of such determination shares of Common Stock issuable upon exercise of the warrants which have not been exercised. The number of shares in the second column does not reflect this limitation. Percentage ownership is based on 28,000,824 shares of Common Stock outstanding as of August 31, 2024.

The information in the following table has been provided to us by or on behalf of the Selling Stockholders and the Selling Stockholders may have sold, transferred or otherwise disposed of all or a portion of their securities after the date on which they provided us with information regarding their securities. Any changed or new information given to us by the Selling Stockholders, including regarding the identity of, and the shares held by, each Selling Stockholder, will be set forth in a prospectus supplement or amendments to the registration statement of which this prospectus is a part, if and when necessary. The Selling Stockholders may sell all, some or none of their shares in this offering. See "Plan of Distribution."

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Relationship with Selling Stockholders

On April 8, 2020, we entered into a Board Appointment Agreement, dated as of April 8, 2020, with Rosalind, pursuant to which Steven Salamon and Gil Aharon, who are principals of Rosalind, were appointed as directors of the Company's Board.

Other than this relationship with Rosalind, none of the Selling Stockholders have had a material relationship with us or any of our predecessors or affiliates within the past three years, other than as a result of the ownership of our shares of Common Stock or other securities.

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PLAN OF DISTRIBUTION

Each Selling Stockholder of the securities and any of their pledgees, assignees and successors-in-interest may, from time to time, sell any or all of their securities covered hereby on the principal trading market (any of the markets or exchanges on which the Common Stock is listed or quoted for trading on the date in question: the NYSE American, The Nasdaq Capital Market, The Nasdaq Global Market, The Nasdaq Global Select Market, The New York Stock Exchange, OTCQB or OTCQX, or the "Pink Sheets" published by OTC Markets Group, Inc. or any successors to any of the foregoing) or any other stock exchange, market or trading facility on which the securities are traded or in private transactions. These sales may be at fixed or negotiated prices. The Company will not receive any of the proceeds from the sale by the Selling Stockholders of the shares offered by this prospectus. A Selling Stockholder may use any one or more of the following methods when selling securities:

The Selling Stockholders may also sell securities under Rule 144 or any other exemption from registration under the Securities Act, if available, rather than under this prospectus.

Broker-dealers engaged by the Selling Stockholders may arrange for other brokers-dealers to participate in sales. Broker-dealers may receive commissions or discounts from the Selling Stockholders (or, if any broker-dealer acts as agent for the purchaser of securities, from the purchaser) in amounts to be negotiated, but, except as set forth in a supplement to this Prospectus, in the case of an agency transaction not in excess of a customary brokerage commission in compliance with FINRA Rule 5110.

In connection with the sale of the shares offered by this prospectus, the Selling Stockholders may enter into hedging transactions with broker-dealers or other financial institutions, which may in turn engage in short sales of the securities in the course of hedging the positions they assume. The Selling Stockholders may also sell securities short and deliver these securities to close out their short positions, or loan or pledge the securities to broker-dealers that in turn may sell these securities. The Selling Stockholders may also enter into option or other transactions with broker-dealers or other financial institutions or create one or more derivative securities which require the delivery to such broker-dealer or other financial institution of securities offered by this prospectus, which securities such broker-dealer or other financial institution may resell pursuant to this prospectus (as supplemented or amended to reflect such transaction).

The Selling Stockholders and any broker-dealers or agents that are involved in selling the securities may be deemed to be "underwriters" within the meaning of the Securities Act in connection with such sales. In such event, any commissions received by such broker-dealers or agents and any profit on the resale of the securities purchased by them may be deemed to be underwriting commissions or discounts under the Securities Act. Each Selling Stockholder has informed the Company that it does not have any written or oral agreement or understanding, directly or indirectly, with any person to distribute the securities.

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The Company is required to pay certain fees and expenses incurred by the Company incident to the registration of the securities. The Company has agreed to indemnify the Selling Stockholders against certain losses, claims, damages and liabilities, including liabilities under the Securities Act.

We agreed to keep this prospectus effective until the earlier of (i) the date on which the securities may be freely resold by the Selling Stockholders without registration and without regard to any volume or manner-of-sale limitations by reason of Rule 144, without the requirement for the Company to be in compliance with the current public information under Rule 144 under the Securities Act or any other rule of similar effect or (ii) all of the securities have been sold pursuant to this prospectus or Rule 144 under the Securities Act or any other rule of similar effect, under circumstances in which any legend borne by such securities relating to restrictions on transferability thereof, under the Securities Act or otherwise, is removed. The Registered Shares will be sold only through registered or licensed brokers or dealers if required under applicable state securities laws. In addition, in certain states, the resale securities covered hereby may not be sold unless they have been registered or qualified for sale in the applicable state or an exemption from the registration or qualification requirement is available and is complied with.

Under applicable rules and regulations under the Exchange Act, any person engaged in the distribution of the resale securities may not simultaneously engage in market making activities with respect to the securities for the applicable restricted period, as defined in Regulation M, prior to the commencement of the distribution. In addition, the Selling Stockholders will be subject to applicable provisions of the Exchange Act and the rules and regulations thereunder, including Regulation M, which may limit the timing of purchases and sales of the securities by the Selling Stockholders or any other person. We will make copies of this prospectus available to the Selling Stockholders and have informed them of the need to deliver a copy of this prospectus to each purchaser of the securities at or prior to the time of the sale (including by compliance with Rule 172 under the Securities Act).

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LEGAL MATTERS

McCarter & English LLP, Newark, New Jersey has passed upon the validity of the shares of Common Stock offered by this prospectus. Certain legal matters with respect to the shares of Common Stock offered by this prospectus will be passed upon by Cooley LLP, Boston, Massachusetts. Additional legal matters may be passed upon for us or any underwriters, dealers or agents, by counsel that we will name in the applicable prospectus supplement.

EXPERTS

The consolidated financial statements as of December 31, 2023 and 2022 and for each of the two years in the period ended December 31, 2023 incorporated by reference in this prospectus have been so incorporated in reliance on the report of Marcum, LLP, an independent registered public accounting firm, incorporated herein by reference, given on the authority of said firm as experts in auditing and accounting.

WHERE YOU CAN FIND MORE INFORMATION;

INCORPORATION BY REFERENCE

Available Information

We file reports, proxy statements and other information with the SEC. The SEC maintains a website that contains reports, proxy and information statements and other information about issuers, such as us, who file electronically with the SEC. The address of that website is www.sec.gov. You may access these materials free of charge as soon as reasonably practicable after they are electronically filed with or furnished to the SEC.

Our website address is http://www.delcath.com. The information on our website, however, is not, and should not be deemed to be, a part of, or incorporated by reference in, this prospectus.

This prospectus and any prospectus supplement are part of a registration statement that we filed with the SEC and do not contain all of the information in the registration statement. The full registration statement may be obtained from the SEC or us, as provided above. Statements in this prospectus or any prospectus supplement about these documents are summaries and each statement is qualified in all respects by reference to the document to which it refers. You should refer to the actual documents for a more complete description of the relevant matters. You may inspect a copy of the registration statement through the SEC's website, as provided above.

Incorporation by Reference

The SEC allows us to incorporate by reference into this prospectus the information contained in other documents we file with the SEC, which means that we can disclose important information to you by referring you to those documents. Any statement contained in any document incorporated or deemed to be incorporated by reference herein shall be deemed to be modified or superseded, for purposes of this prospectus, to the extent that a statement contained in or omitted from this prospectus, or in any other subsequently filed document that also is or is deemed to be incorporated by reference herein, modifies or supersedes such statement. Any such statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus. We incorporate by reference the documents listed below which have been filed by us:

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All documents we file with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act, except as to any portion of any report or documents that is not deemed filed under such provisions, (1) on or after the date of filing of the registration statement containing this prospectus and prior to the effectiveness of the registration statement and (2) on or after the date of this prospectus until the earlier of the date on which all of the securities registered hereunder have been sold or the registration statement of which this prospectus is a part has been withdrawn, shall be deemed incorporated by reference in this prospectus and to be a part of this prospectus from the date of filing of those documents and will be automatically updated and, to the extent described above, supersede information contained or incorporated by reference in this prospectus and previously filed documents that are incorporated by reference in this prospectus.

Nothing in this prospectus shall be deemed to incorporate information furnished but not filed with the SEC pursuant to Item 2.02, 7.01 or 9.01 of Form 8-K. Upon written or oral request, we will provide without charge to each person, including any beneficial owner, to whom a copy of the prospectus is delivered a copy of any or all of the reports or documents incorporated by reference herein (other than exhibits to such documents, unless such exhibits are specifically incorporated by reference herein). You may request a copy of these filings, at no cost, by writing or telephoning us at the following address: Delcath Systems, Inc., 566 Queensbury Avenue, Queensbury, NY 12804.

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