[2] Prior to turning professional, Petersen played college ice hockey for the University of Notre Dame.

He set an NCAA Division I record of 87 saves during the longest collegiate ice hockey game ever.

[1] He helped lead Notre Dame to the Hockey East playoffs, playing in all six games.

[9] On May 31, 2017, Petersen announced he was forgoing his final year of college eligibility, giving the Sabres 30 days to sign him before he became a free agent.

On July 1, 2017, he signed a two-year, entry-level contract with the Los Angeles Kings as an unrestricted free agent.

[12] Petersen made his NHL debut the following night against the Toronto Maple Leafs, coming in to relieve starter Peter Budaj in the second period.

[15] Two games later, on November 19, Petersen recorded his first career NHL shutout by making 29 saves in a 2–0 win over the St. Louis Blues.

[21] On May 4, 2023, Petersen was named to the United States men's national ice hockey team to compete at the 2023 IIHF World Championship.