The release of Jeff Mizanskey followed years of lobbying from family, lawmakers, and advocates for the legalisation of marijuana, who argued that the sentence was too stiff.
Mizanskey was sentenced in 1996 after police said he conspired to sell 2.7kg of marijuana to a dealer connected to Mexican drug cartels.
The life with no parole sentence was allowed under a Missouri law for persistent drug offenders. Mizanskey already had two drug convictions — one for possession and sale of marijuana in 1984 and another for possession in 1991.
Mizanskey was the only Missouri inmate serving such a sentence for a non-violent marijuana-related offence when Democratic governor Jay Nixon agreed in May to commute his sentence.
Nixon’s action allowed Mizanskey to argue for his freedom.
Nixon cited Mizanskey’s non-violent record, noting that none of his offences involved selling drugs to children.