With no background in sports, Collier started Brazilian jiu-jitsu to lose weight at the age of 20. Eventually he started competing in the sport and ended up to an amateur mixed martial arts bout.
After compiling an amateur record of 12–2, Collier made his professional debut in November of 2010. He competed primarily for regional organizations around his native state of Missouri. He amassed a record of 7–1 before signing with the UFC on the heels of a first round finish of Gabriel Checco at RFA 19.
Collier made his promotional debut against Vitor Miranda on December 20, 2014 at UFC Fight Night 58. He lost the fight via TKO in the final seconds of the first round. Collier next faced Ricardo Abreu on June 6, 2015 at UFC Fight Night 68, filling in for an injured Daniel Sarafian. Collier won the fight via split decision. Collier faced returning veteran Dongi Yang on November 28, 2015 at UFC Fight Night 79. He lost the fight via TKO in the second round. Collier next faced promotional newcomer Alberto Uda on May 29, 2016 at UFC Fight Night 88. He won the fight via TKO in the second round and was awarded a Performance of the Night bonus. Collier was expected to face Josh Stansbury in a light heavyweight bout on December 3, 2016 at. However, Collier pulled out of the fight in late October citing injury and was replaced by Devin Clark. Collier faced Devin Clark on April 15, 2017 at UFC on Fox 24. He lost the fight by unanimous decision. Collier faced Marcel Fortuna on November 11, 2017 at. He won the fight by unanimous decision. Collier was scheduled to face Marin Prachnio on February 24, 2018 at UFC on Fox 28. However, on January 4, 2018, he was forced to pull out from the fight citing injury. On February 16, 2019 it was announced that Collier had tested positive for higenamine in an out of competition test for which he received a ten month suspension and he will be eligible to compete again on October 27, 2019. Collier was scheduled to face Tom Aspinall in a heavyweight bout on March 21, 2020 at after more than two years absence from UFC. However, due to COVID-19 pandemic, the event was cancelled. Subsequently, the pairing was left intact and took place on July 25, 2020 at UFC on ESPN 14. He lost the fight via technical knockout in round one.
