Exhibit 23.1

Independent Registered Public Accounting Firm’s Consent

We consent to the incorporation by reference in this Registration Statement of Delcath System, Inc. and Subsidiaries on Form S-1 Amendment No. 3 (File No. 333-233396), Form S-1 Amendment No. 1 (File No. 333-235751), Form S-1 Amendment No. 2 (File No. 333-235904), Form S-1 Amendment No. 2 (File No. 333-236100), Form S-3 (File No. 333-227970), and Form S-8 (File No. 333-251385) of our report dated March 31, 2021, which includes an explanatory paragraph as to the Company’s ability to continue as a going concern, with respect to our audits of the consolidated financial statements of Delcath System, Inc. and Subsidiaries as of December 31, 2020 and 2019 and for each of the two years ended December 31, 2020 appearing in the Annual Report on Form 10-K of Delcath System, Inc. and Subsidiaries for the year endedDecember 31, 2020.

/s/ Marcum LLP

Marcum LLP

New York, NY

March 31, 2021