He attended Ozen High School. He was selected to the 4A all-state second-team in his senior year in high school. He was selected to the First-team All-District 20-4 and Port Arthur News Super Team while at high school.
College career
He started his career as a wide receiver at Baylor University but was kicked off of the team after he and teammate Josh Gordon were found asleep in Jefferson's car at a local Taco Bell with marijuana in the car. Jefferson, who was driving, was kicked off the team due to it being his second violation. He transferred to Stephen F Austin and was named 2011 Southland Conference Newcomer of the Year in his Junior season. He led the Southland Conference in sacks with 16. He was selected to the Sports Network All-America second team, Phil Steele's Magazine All-America third team.
In 2014, Jefferson signed with the Edmonton Eskimos of the Canadian Football League. Jefferson played for two seasons with the Eskimos, playing in 35 games, contributing 40 defensive tackles, 10 quarterback sacks, and three forced fumbles.
Washington Redskins
Jefferson signed a futures contract with the Washington Redskins on January 14, 2016. On August 27, 2016, Jefferson was waived by the Redskins.
Saskatchewan Roughriders
In September 2016, Jefferson returned to the CFL and signed with the Saskatchewan Roughriders rejoining his head coach from Edmonton. Jefferson was named a CFL All-Star in 2017, and in 2018 was nominated as the teams Most Outstanding Player and Most Outstanding Defensive Player after recording his first season with double digit sacks, and a pair of interceptions returned for touchdowns. Jefferson was again named to the CFL All-Star Team alongside teammate Charleston Hughes.
Winnipeg Blue Bombers
On February 12, 2019, it was announced that Jefferson had signed a one-year deal with the Winnipeg Blue Bombers through the 2019 season. 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. Jefferson's most notable performance came against Edmonton, where he recorded four tackles, three sacks, two forced fumbles, recovered another fumble, knocked down two passes, recovered an onside kick attempt, and scored a rouge when he kicked a fumble through the endzone. By season's end, Jefferson played in all 18 games and made 24 tackles and caught an interception; he also set new career highs for sacks and forced fumbles, with 12 and 6 respectively, he also set the CFL record for a defensive lineman with 16 pass knockdowns. Jefferson's strong play in the playoffs, together with his fellow defensive linemen Jackson Jeffcoat, Drake Nevis, and Jake Thomas saw the Bombers defence control the games against the Calgary Stampeders and Saskatchewan Roughriders, to lead the Bombers to the 107th Grey Cup. In the championship game Jefferson had two tackles, three sacks, two forced fumbles, with a dominant performance that saw the Bombers end their 29 year Grey Cup drought. After the game he said that "I just had to come out here and give it my all. I had my dad, my mom, my wife and my daughter. I couldn't come out here and play a mediocre game in front of my family." For the second consecutive year, Jefferson won the award for both Most Outstanding Player, and Defensive Player for his team, he ultimately won the CFL Most Outstanding Defensive Player Award for his performance over the course of the 2019 CFL season. Prior to the next season, Jefferson signed a two year contract extension keeping him in Winnipeg through the 2021 season at approximately $265,000 a year.
