| Cover | Jan. 10, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jan. 10, 2022 |
| Entity File Number | 001-38596 |
| Entity Registrant Name | REPLIMUNE GROUP, INC. |
| Entity Central Index Key | 0001737953 |
| Entity Tax Identification Number | 82-2082553 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 500 Unicorn Park |
| Entity Address, City or Town | Woburn |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 01801 |
| City Area Code | 781 |
| Local Phone Number | 222-9600 |
| 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 per share |
| Trading Symbol | REPL |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | true |
