He registered 24 points (three goals and 21 assists) and was named to the Central Collegiate Hockey Association (CCHA) All-Rookie Team in his freshman year.

He achieved a significant improvement to his game for his junior year at Michigan State, however, as he finished third overall in team scoring and first as a defenseman, collecting 29 points (four goals and 25 assists).

[14] Expectations were high based on four consecutive forty point seasons, but Petry's struggles became one of the most prominent features of a historically poor start for the team.

In his first 25 games, Petry recorded only 2 secondary assists, and committed numerous miscues that attracted commentator and fan speculation that he was attempting to play through injury.

[16] In December, shortly after the sacking of longtime general manager Marc Bergevin, the team announced that Petry was dealing with an upper body injury and would miss an undetermined number of upcoming games.

[17] The change in management with the hiring of Jeff Gorton and possibility of the Canadiens initiating a long-term rebuild raised questions about whether Petry would seek a trade.

[19] His situation became more complicated still when his wife Julie became frustrated with the Quebec government's pandemic measures and relocated with their children to Detroit for the remainder of the season.

[20] Following Ducharme's sacking by new general manager Kent Hughes and the hiring of Martin St. Louis to replace him, Petry's play markedly improved.

[20] Petry subsequently sustained a lower body injury in a March 24 game against the Florida Panthers, exiting in the third period, and was announced as being out indefinitely.

[21] After returning, he played what was widely judged as his best hockey of the season in the final weeks of April, including a two-goal performance to help the team beat the New York Rangers 4–3, snapping a nine-game losing streak in the penultimate game of the year.

[16] On July 16, 2022, Petry, along with forward Ryan Poehling, was traded to the Pittsburgh Penguins in exchange for Mike Matheson and a 2023 fourth-round draft pick.

His father, Dan Petry, is a former Major League Baseball (MLB) pitcher who earned a World Series ring as a member of the Detroit Tigers in 1984.