Filed Pursuant to Rule 424(b)(3)
Registration No. 333-272659
PROSPECTUS SUPPLEMENT NO. 1
(To Prospectus Dated June 28, 2023)
Up to 19,509,302 Shares of Common Stock Offered by the Selling Stockholders
This Prospectus Supplement No. 1 (this Prospectus Supplement) is being filed to update and supplement the information contained in the
Selling Stockholders section of the Delcath Systems, Inc. (the Company) prospectus, dated June 14, 2023 (as may be amended and supplemented from time to time, the Prospectus). The Prospectus, as supplemented
by this Prospectus Supplement, relates to the offer and resale from time to time by certain selling stockholders named in the Prospectus of up to 19,509,302 shares of Companys common stock, par value $0.01 per share (the Common
Stock), which consist of (i) 2,915,908 shares of Common Stock, issuable upon conversion of 9,622 shares of Series F-2 Convertible Preferred Stock, par value $0.01 per share (the Series F-2 Preferred Stock), (ii) 7,746,437 shares of Common Stock issuable upon conversion of 34,860 shares of F-3 Preferred Stock exercisable pursuant to the preferred stock
tranche A warrants (the Preferred Tranche A Warrant) to acquire shares of Series F-3 Preferred Stock, par value $0.01 per share (the Series F-3
Preferred Stock), (iii) 4,149,995 shares of Common Stock issuable upon conversion of 24,900 shares of F-4 Preferred Stock exercisable pursuant to the preferred stock tranche B warrants (the
Preferred Tranche B Warrant, together with the Preferred Tranche A Warrant, the Preferred Warrants) to acquire shares of Series F-4 Preferred Stock, par value $0.01 per share (the
Series F-4 Preferred Stock and together with the Series F-3 Preferred Stock, the Preferred Warrant Shares), (iv) 4,649,186 shares of Common
Stock, (v) 31,110 shares of Common Stock, issuable upon exercise of the common stock tranche A warrants (Common Tranche A Warrant), and (vi) 16,666 shares of Common Stock issuable upon exercise of common stock tranche B warrants (the
Common Tranche B Warrant, together with the Common Tranche A Warrant, the Common Warrants, and together with the Preferred Warrants, the Warrants).
This Prospectus Supplement is being filed to amend the selling stockholder information set forth in the Prospectus as set forth on Annex A attached
hereto. This Prospectus Supplement should be read in conjunction with the Prospectus and if there is any inconsistency in the information in the Prospectus and this Prospectus Supplement, you should relay on the information in this Prospectus
Supplement. This Prospectus Supplement is not complete without, and may not be delivered or used except in connection with, the Prospectus.
Our Common
Stock is listed on The Nasdaq Capital Market under the symbol DCTH. On August 31, 2023, the closing price for our Common Stock, as reported on The Nasdaq Capital Market, was $4.59 per share.
Investing in our securities involves certain risks. See Risk Factors on page 6 of the Prospectus. See also Risk Factors contained
in any amendments or supplements to the Prospectus and in the documents incorporated by reference in the Prospectus.
Neither the Securities and
Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if the Prospectus and this Prospectus Supplement, is truthful or complete. Any representation to the contrary is a criminal
offense.
The date of this Prospectus Supplement is September 1, 2023.