Campbell was chosen by the Dallas Stars with the No. 11 pick in the 2010 NHL Draft. He was the first goalie taken. Campbell spent seven seasons in the Stars organization, playing one NHL game, before being traded to the Los Angeles Kings for defenseman Nick Ebert on June 25, 2016.After playing most of the next two seasons with Ontario of the American Hockey League, Campbell earned his first NHL win by making 41 saves in a 4-1 victory against the Vegas Golden Knights on Feb. 27, 2018, his first NHL start since Oct. 20, 2013. He appeared in five games, going 2-0-2 with a 2.47 goals-against average and .924 save percentage while backing up Jonathan Quick."This is the opportunity I've always wanted and worked for," Campbell told LAKings.com on March 13, 2018. "Now that it's here I just have to do everything I can to enjoy it and work as hard as I can to be ready."Campbell finished 2018-19 with a 2.30 GAA despite a 10-14-1 record. He appeared to have settled into a backup role behind Jonathan Quick with Los Angeles until being traded to the Toronto Maple Leafs on Feb. 5, 2020.