The Montreal lightweight (28-1) dropped Dominican Carlos Manuel Reyes (24-4-1) with a left to the body in the third round of a scheduled 10 round bout to claim the victory on Saturday night at the Bell Centre.
The fight was on the undercard of Canadian Jean Pascal's bid to oust the WBA, WBO and IBF light heavyweight titles from Russian Sergey Kovalev, to be held later Saturday.
Jean entered rehab for alcohol and gambling addictions in November. He said he has never felt better, in and out of the ring.
"We've been sober for 133 days, training hard, committed to the gym, " the 32-year-old said. "It's a lot different.
"Now I'm going to eat and maybe see my girlfriend and then go home. Usually, it's go party. But no more party."
It was a third win in a row since his January, 2014 loss to Lamont Peterson for the IBF title. Now he hopes to get back in contention for another title shot.
He had little trouble with Reyes, who has fought most of his career in lighter weight classes.
Jean had him down early in the third and then finished him off.
"My coach (Mike Moffa) asked me to use combinations instead of one punch at a time and when I did that, I stopped him," he said.
In other bouts, light welterweight Junior Ulysse (6-0) of Montreal had no trouble stopping Miguel Antoine (17-2-1) of Barbados in the fifth round and Russian welterweight Dmitry Mikhaylenko (19-0) did the same to Felipe de la Paz (14-4-2) of Mexico.
Nadjib Mohammedi (38-3) of France was all over Lee Junior Campbell (8-2), stopping the American light heavyweight in six rounds.
Welterweight David Theroux (6-0) of Sorel, Que., knocked out Lukasz Janik (12-10-1) of Poland in three.