Cover
| Cover | 12 Months Ended | |
| Mar. 02, 2023 | Dec. 31, 2023 | |
| Cover [Abstract] | ||
| Document Type | 8-K | |
| Entity Registrant Name | SESEN BIO, INC. | |
| Entity Incorporation, State or Country Code | DE | |
| Entity File Number | 001-36296 | |
| Entity Tax Identification Number | 26-2025616 | |
| Entity Address, Address Line One | 245 First Street | |
| Entity Address, Address Line Two | Suite 1800 | |
| Entity Address, City or Town | Cambridge | |
| Entity Address, State or Province | MA | |
| Entity Address, Postal Zip Code | 02142 | |
| City Area Code | 617 | |
| Local Phone Number | 444-8550 | |
| Written Communications | false | |
| Soliciting Material | false | |
| Pre-commencement Tender Offer | false | |
| Pre-commencement Issuer Tender Offer | false | |
| Title of 12(b) Security | Common Stock, par value $0.001 | |
| Trading Symbol | SESN | |
| Security Exchange Name | NASDAQ | |
| Entity Emerging Growth Company | false | |
| Entity Central Index Key | 0001485003 | |
| Current Fiscal Year End Date | --12-31 | |
| Amendment Flag | false | |
| Document Period End Date | Mar. 02, 2023 |