Primus compiled an amateur record of 5-1 before making his professional debut in September 2010, defeating Chris Ensley via first-round submission. In his second pro bout, Primus defeated Roy Bradshaw via submission in the first round on May 12, 2012.
Bellator MMA
Primus signed with Bellator in 2013. He made his debut for the organization on September 27, 2013 at Bellator 101 against Scott Thometz. Primus won via rear-naked choke submission at 3:48 in the first round, improving his record to 3–0. Primus had his second bout with the organization on November 22, 2013 at Bellator 109. He defeated Brett Glass by rear-naked choke submission in the first round. In his next bout, Primus faced Chris Jones at Bellator 111 on March 7, 2014. Primus won via TKO in the first round, which marked the first time Primus had finished an opponent that was not by rear-naked choke. After nearly a year-and-a-half away from the sport, Primus returned to face Derek Anderson at Bellator 141 on August 28, 2015. He won the fight by split decision. Primus next faced Gleristone Santos at Bellator 153 on April 22, 2016. He won the fight by split decision.
With an undefeated streak of five wins in Bellator, Primus faced Bellator Lightweight championMichael Chandler at Bellator NYC on June 24, 2017. At 2:22 in the first round, the bout was temporarily halted by the referee to check on Chandler, whose left ankle was visibly injured. The bout was stopped in favor of Primus via TKO, awarding him the Bellator Lightweight World Championship and pulling off one of the biggest upsets in Bellator history. Primus was expected to make his first title defense against Chandler in a rematch at Bellator 197 on April 13, 2018. However, he pulled out of the fight due to a knee injury. As a result, Brandon Girtz stepped in as a replacement. The rematch between Primus and Chandler finally took place in the main event of Bellator 212 on December 14, 2018. Primus was out-wrestled for the better part of the fight, and despite landing similar leg kicks to those that stopped Chandler in their first fight and dropping Chandler with a punch in the second round, Primus was defeated by Chandler via unanimous decision.
Post-title era
As the first fight after losing his title, Primus faced Tim Wilde at Bellator: Birmingham on May 4, 2019. He won the fight via gogoplata in the first round. Primus was expected to face Peter Queally at Bellator Dublin on February 22, 2020. However, Queally was forced to withdraw from the bout due to knee injury and was subsequently replaced by Chris Bungard. Primus won the bout via neck-crank submission in the 1st round.
