Through his first five NHL stops, from Manhattan to Glendale, Ariz., Boston to Long Island and Buffalo, there had always been one place Johnson dreamed of playing: in the city he considered home, Calgary, wearing a Flames jersey.

Selected by the Pittsburgh Penguins in the fifth round (No. 125) of the 2006 NHL Draft, following his freshman year at the University of Alaska Fairbanks, Johnson didn't appear in a game in the Pittsburgh organization, playing four college seasons instead. As a senior in 2008-09, he had a 1.66 goals-against average and .940 save percentage. He was named a Hobey Baker Award finalist and the Central Collegiate Hockey Association Player of the Year that season.

The Penguins traded Johnson to the New York Rangers in June 2009 for a fifth-round draft pick. During three seasons in the Rangers organization, Johnson appeared in six games, playing mostly with its American Hockey League affiliates.

Johnson signed with the Phoenix Coyotes for the 2012-13 season, making four starts, then signed a one-year contract with the Boston Bruins in July of 2013.

As a backup to Tuukka Rask in 2013-14, Johnson played 27 games and had a 17-4-3 record, 2.10 GAA and .925 save percentage. Johnson then moved on to the New York Islanders and then the Buffalo Sabres over the next two seasons, setting a team record for the most saves in a regulation shutout with 44 in a win against the Anaheim Ducks on Dec. 17, 2015.

As an unrestricted free agent, Johnson fulfilled his long-held dream by signing with the Flames on July 1, 2016.