A Michigan man serving up to 60 years in prison for selling 3 pounds of marijuana to an undercover informant is pleading for clemency — a desperate bid to avoid what supporters say amounts to a “life sentence.”

Michael Alonzo Thompson, 68, has spent more than 25 years in prison after being convicted of selling pot and possessing firearms as a felon in Genesee County in December 1994, according to a website seeking his immediate release.

“He has been in prison ever since,” the site reads. “It has been 25 years. And he still has 35 years left to serve … In other words, he was given a life sentence for selling weed.”

Thompson’s earliest release date from the Muskegon Correctional Facility is in April 2038, but he could be kept behind bars until February 2047 — some 53 years after the 1994 crime. His maximum sentence is listed as 60 years, according to prison records.

Thompson’s attorney, Kimberly Kendall Corral, said she submitted a petition of clemency Wednesday on his behalf to the Michigan Department of Corrections Parole Board, his third attempt. His last request for release was denied by then-Gov. Rick Snyder in 2018 — the same year Michigan voted to legalize recreational marijuana in the state.

A copy was also sent overnight to Gov. Gretchen Whitmer, who cannot make a recommendation until after the parole board determines whether commutation of Thompson’s sentence is warranted, Corral said.

“This is his third application for commutation,” Corral told The Post. “The issue we ran into this case was not less egregious than it was two years ago when Gov. Snyder denied it.”

More than 21,000 people had signed Thompson’s clemency petition as of Thursday. A message seeking comment from Whitmer’s office was referred to the state’s parole board. A spokesman for that agency did not immediately return a message Thursday afternoon.

“By the end of 2021 recreational weed is projected to be a $1.5 billion industry in Michigan,” Thompson’s website reads. “But Michael has literally spent almost half of his life in prison for selling weed. It has cost the state of Michigan over a million dollars to keep him there.”

The length of Thompson’s sentence is attributable to his prior drug-related felony convictions, a Michigan Department of Corrections spokesman told WZZM.

“They were able to charge him as a habitual offender, which means they can add on increased years to his sentence,” spokesman Chris Gautz said.

Gautz said Thompson has been a model prisoner, citing only two minor infractions in the last quarter-century.

“Some prisoners, who maybe aren’t as well adjusted, might have two tickets in a week, so to only have two in two decades is a pretty small number,” Gautz told the station.

Thompson’s attorney, meanwhile, said her client is hopeful but has reservations because the criminal justice system has failed him many times before, she said.

“Not everyone is super hopeful,” Corral said. “We’ve seen so many injustices that it’s hard to trust the system to work like it’s intended.”