[2] Jefferson started his college football career as a wide receiver for the Baylor Bears in 2009 and moved to tight end for the 2010 season.

Jefferson transferred to Stephen F. Austin University to play for the Lumberjacks and was named 2011 Southland Conference Newcomer of the Year in his Junior season.

[9] In 2015, Jefferson played in all 18 regular season games, starting in six, where he had 24 defensive tackles, six sacks, four pass knockdowns, and three forced fumbles.

[13] On September 28, 2016, Jefferson returned to the CFL and signed with the Saskatchewan Roughriders, rejoining his former head coach from Edmonton, Chris Jones.

[9] Jefferson was named a CFL All-Star in 2017 after he played and started in all 18 regular season games and had a career-high 45 defensive tackles along with eight sacks, six knockdowns, and one fumble recovery for a touchdown.

[15] For his strong season, Jefferson was again named to the CFL All-Star Team alongside teammate Charleston Hughes.

[18] Jefferson felt the Roughriders' offer did not match his market value; he was also courted by the Toronto Argonauts, but signed with the Blue Bombers for $210,000 CND.

[20] By season's end, Jefferson played in all 18 games and made 25 defensive tackles and caught an interception; he also set new career highs for sacks and forced fumbles, with 12 and six respectively.

Winnipeg finished the season with the best record in the CFL and Jefferson and the Bombers defence led the league in fewest yards and points allowed.

After the extra time win, Jefferson said that "We're behind enemy lines, fans on our backs, city against us and we had to come out here and show these guys who we are.

"[28] Jefferson continued his stellar play in the 2022 CFL season, contributing with 33 defensive tackles, seven sacks, two forced fumbles, one interception and one touchdown.

[29] In 2023, Jefferson played and started in 17 regular season games where he recorded 21 defensive tackles, 11 sacks, a league-leading 13 pass knockdowns, and three forced fumbles.

He played in his fifth Grey Cup game, and fourth consecutively, where he had one defensive tackle and one sack, but the Blue Bombers were defeated by the Montreal Alouettes.