Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2021	Aug. 13, 2021
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Jun. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Current Fiscal Year End Date	--12-31
Entity File Number	000-56075
Entity Registrant Name	4Front Ventures Corp.
Entity Incorporation, State or Country Code	A1
Entity Tax Identification Number	83-4168417
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
Trading Symbol	FFNT
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Shell Company	false
Entity Ex Transition Period	false
Entity Common Stock Shares Outstanding		592,627,966
Entity Central Index Key	0001783875
Amendment Flag	false
Class A Subordinate Voting Shares
Document Information [Line Items]
Trading Symbol	FFNTF
Title of 12(g) Security	Class A Subordinate Voting Shares, no par value