Originally undrafted by teams in the National Hockey League (NHL), Flynn has previously played for the Buffalo Sabres and Montreal Canadiens.

[5] After two and a half seasons with the Canadiens, Flynn left as a free agent and signed a one-year, two-way contract with the Dallas Stars on July 1, 2017.

[citation needed] As a free agent from the Stars, Flynn opted to sign a one-year, two-way contract with the St. Louis Blues on July 1, 2018.

[8] On January 21, 2019, Flynn agreed to his first European contract, joining Swiss club EV Zug of the National League (NL) on a one-year deal through the end of the 2018–19 season.

After three seasons abroad in Switzerland, Flynn returned to North America as a free agent, securing a one-year, two-way deal with the New Jersey Devils on July 29, 2021.