After briefly returning to junior hockey, he finished the 1953–54 season playing his first three professional games with the Cleveland Barons.

His first complete professional season was in 1954–55, with the Troy Bruins in the International Hockey League, scoring 25 goals.

[4] Mortson played two and a half seasons in the EPHL with Sudbury, and still had the fourth most assists, and eighth most points in the history of the four-year league.

He scored a personal best 33 goals in the 1965–66 season, finished second in the league with 95 points, and was named an AHL second team all-star.

At age 34, he played in all 72 games that regular season, and in the playoffs won his first team championship as a player, winning the Lester Patrick Cup, as champions of the Western Hockey League.

Playing with Dallas, his team reached the Adams Cup finals in the Central Hockey League, but lost in six games.

The World Hockey Association was founded in 1972, and Mortson at age 38, made his major league debut with the Houston Aeros in the 1972–73 season.

[12] Mortson was the team's leading scorer, with 24 goals, and 51 assists in 59 games, and was also the first hockey player to wear the number 99.

[12] When the Whoopees folded in February due to financial issues, Mortson had led the team to 22 wins in 62 games.

[14] After taking a year off, at age 42 Mortson played 16 games including playoffs, for the Buffalo Norsemen of the North American Hockey League.

In 1985, he coached the North Bay Sun Life team to an Ontario Baseball Association midget championship.