Bellator Fighting Championships Pierson was set to compete in Bellator's Second Season Welterweight Tournament but an injury forced him out of the tournament. He was set to have his first fight against
Dan Hornbuckle which would have taken place at
Bellator 15.
Ultimate Fighting Championship After
TJ Waldburger had to pull out of his fight with
Matthew Riddle at
UFC 124 due to injury, it was announced on October 27 that Pierson had signed with the
UFC to step in on short notice. After outstriking Riddle over three fast-paced rounds, Pierson won a unanimous decision (30–27, 30–27, 30–27). The fight was dubbed by
Dana White as the real
Fight of the Night. Pierson was expected to face
Brian Foster on April 30, 2011, at
UFC 129. However, Foster was forced out of the bout with an injury, and replaced by
Jake Ellenberger. Pierson lost to Ellenberger via first-round KO after he was caught by a counter left. Pierson fought
Dong Hyun Kim on December 30, 2011, at
UFC 141. Pierson was defeated by Kim via unanimous decision (30-27, 30-27, 30-27). Pierson defeated
Jake Hecht by unanimous decision on June 8, 2012, at
UFC on FX 3. Pierson was expected to face
Dan Miller on September 22, 2012, at
UFC 152. However, Miller pulled out of the bout after getting news about his son's kidney transplant operation and was replaced by
Lance Benoist. Pierson defeated Benoist via unanimous decision. Pierson was expected to face
Rick Story on March 16, 2013, at
UFC 158. However, he was forced out of the bout with an injury and replaced by
Quinn Mulhern. Pierson was expected to face
TJ Waldburger on June 15, 2013, at
UFC 161. However, Waldburger was pulled from the event and replaced by
Kenny Robertson. Despite being hurt in the third round, Pierson won the fight by majority decision. ==Personal life==