Petersen was originally drafted by the Buffalo Sabres with the 129th overall selection in the fifth round but ultimately did not sign with them. Following Petersen's three-year career at Notre Dame, the tendy signed with the Kings as a free agent on July 1, 2017.
Between 2017-2020, Petersen would work as the back-stop for the Kings AHL affiliate, Ontario Reign. In 116 games, Petersen went 53-51-7 and recorded a save percentage north of .900.
During his tenure with the Reign, Petersen made his NHL debut on November 13, 2018 in relief of Peter Budaj. In the 35 minutes that Petersen played, the rookie made 16 saves, allowing just one goal. Three days later, Petersen made his first career NHL start in Chicago, where part of his youth career took off. In an overtime thriller, Petersen stopped 35-36 shots in a 2-1 victory for the Kings.