On March 28, 2017, having completed his junior season with the Friars in 2016–17, Walman concluded his collegiate career early, signing a three-year, entry-level contract with the St. Louis Blues.

On March 21, 2022, Walman was traded to the Detroit Red Wings, along with Oskar Sundqvist, and a second-round pick in 2023 NHL Entry Draft, in exchange for Nick Leddy and Luke Witkowski[4] On August 11, 2022, Walman as a restricted free agent was re-signed by the Red Wings to a one-year, $1.05 million contract extension for the 2022–23 season.

[5] After opening the season on the injured-reserve, Walman returned and was given an increased role on the team, playing alongside Moritz Seider.

[7] On June 25, 2024, he was traded to the San Jose Sharks, along with a second-round pick in the 2024 NHL entry draft, in exchange for future considerations.

Following the ruling, Walman was invited to the Canadian men’s national junior ice hockey team’s selection camp, but did not make the final roster.