Selected by the Detroit Red Wings in the fifth round (No. 141) of the 2010 NHL Draft, Mrazek won 62 games over his last two seasons with Ottawa of the Ontario Hockey League before turning pro for the 2012-13 season.

He won his NHL debut with the Red Wings against the St. Louis Blues on Feb. 7, 2013, but later returned to the American Hockey League and helped Grand Rapids win the Calder Cup.

After going 27-16-6 with a 2.33 goals-against average and .921 save percentage in 54 games for the Red Wings in 2015-16, Mrazek signed a two-year contract with Detroit on July 27, 2016. He played 72 games over nearly two more seasons before he was traded by the Red Wings to the Philadelphia Flyers for two conditional draft picks on Feb. 19, 2018. He went 6-6-3 with a 3.22 GAA in 17 games for Philadelphia.

Mrazek signed a one-year contract with the Hurricanes on July 1, 2018. He reclaimed his role as a No. 1 goalie, going 23-14-3 with a 2.39 GAA and .914 save percentage and helped Carolina reach the Eastern Conference Final.

After two more seasons in Carolina, Mrazek signed a three-year, $11.4 million contract ($3.8 million average annual value) with the Toronto Maple Leafs on July 28, 2021.

NOTES & TRANSACTIONS

• AHL Second All-Star Team (2014)
• Traded to Philadelphia by Detroit for a conditional pick in 2018 NHL Draft and a conditional pick in 2019 NHL Draft, February 19, 2018.
• Signed as a free agent by Carolina, July 2, 2018.
• Signed as a free agent by Toronto, July 28, 2021.
• Traded to Chicago by Toronto with a 1st-round pick in the 2022 NHL Draft for a 2nd-round pick in 2022, July 7, 2022.