| Cover | Aug. 16, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Aug. 16, 2021 |
| Entity File Number | 000-56075 |
| Entity Registrant Name | 4FRONT VENTURES CORP. |
| Entity Central Index Key | 0001783875 |
| Entity Tax Identification Number | 83-4168417 |
| Entity Incorporation, State or Country Code | A1 |
| Entity Address, Address Line One | 5060 N. 40th Street |
| Entity Address, Address Line Two | Suite 120 |
| Entity Address, City or Town | Phoenix |
| Entity Address, State or Province | AZ |
| Entity Address, Postal Zip Code | 85018 |
| City Area Code | 602 |
| Local Phone Number | 633-3067 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Class A Subordinate Voting Shares, no par value |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | false |
