| Document and Entity Information - USD ($) $ in Millions | 12 Months Ended | ||
| Dec. 31, 2020 | Mar. 10, 2021 | Jun. 30, 2020 | |
| Cover [Abstract] | |||
| Document Type | 10-K/A | ||
| Amendment Flag | true | ||
| Amendment Description | Amendment No. 1 | ||
| Entity Shell Company | false | ||
| Document Period End Date | Dec. 31, 2020 | ||
| Document Fiscal Year Focus | 2020 | ||
| Document Fiscal Period Focus | FY | ||
| Trading Symbol | ACET | ||
| Security Exchange Name | NASDAQ | ||
| Title of 12(b) Security | Common Stock, par value $0.0001 per share | ||
| Entity Registrant Name | Adicet Bio, Inc. | ||
| Entity Central Index Key | 0001720580 | ||
| Current Fiscal Year End Date | --12-31 | ||
| Entity Well-known Seasoned Issuer | No | ||
| Entity Current Reporting Status | Yes | ||
| Entity Interactive Data Current | Yes | ||
| Entity Voluntary Filers | No | ||
| Entity Filer Category | Non-accelerated Filer | ||
| Entity Common Stock, Shares Outstanding | 31,780,347 | ||
| Entity Small Business | true | ||
| Entity Emerging Growth Company | true | ||
| Entity Ex Transition Period | false | ||
| Entity File Number | 001-38359 | ||
| Entity Tax Identification Number | 81-3305277 | ||
| Entity Public Float | $ 40 | ||
| Entity Address, Address Line One | 200 Clarendon Street | ||
| Entity Address, Address Line Two | Floor 6 | ||
| Entity Address, City or Town | Boston | ||
| Entity Address, State or Province | MA | ||
| Entity Address, Postal Zip Code | 02116 | ||
| Entity Incorporation, State or Country Code | DE | ||
| City Area Code | 857 | ||
| Local Phone Number | 315-5528 | ||
| Document Annual Report | true | ||
| Document Transition Report | false | ||
| ICFR Auditor Attestation Flag | false |
