Prior to signing with Bellator, Pettis competed in the Ultimate Fighting Championship (UFC), where he fought in both the Bantamweight and Flyweight divisions.
[11] Pettis turned pro on September 10, 2011, against Kyle Vivian at Canadian Fighting Championship 7.
[15] Curran was forced out of the bout for personal reasons, RFA President Ed Soares reported that Dillard Pegg will take his place and fight Pettis for the flyweight title.
[20] Pettis was expected to make his promotional debut against Vaughan Lee in a bantamweight bout on November 16, 2013, at UFC 167.
[21] A week before the fight Lee was forced out of the bout due to injury and was replaced by Will Campuzano.
[25] Pettis faced Yaotzin Meza on June 7, 2014, at UFC Fight Night: Henderson vs.
[35] Pettis was expected to face Louis Smolka on October 1, 2016, at UFC Fight Night 96.
[36] However, Pettis pulled out of the fight during the week leading up to the event citing what his trainer described as "a minor injury" and was replaced by promotional newcomer Brandon Moreno.
[37][38] Pettis was expected to face Jussier Formiga on January 15, 2017, at UFC Fight Night 103.
[43] Pettis faced Brandon Moreno on August 5, 2017, in the main event at UFC Fight Night 114.
[52] Pettis faced Rob Font in a bantamweight bout, on December 15, 2018, at UFC on Fox 31.
[58] However, Perez pulled out of the bout on August 26 citing an injury,[59] and he was replaced by Tyson Nam.
[62] Later, news surfaced that Pettis fought out his contract with his previous fight with Nam, and is testing free agency.
[73] However Pettis was forced to pull out of the bout and the Grand Prix after sustaining an injury that required surgery.
[76] Pettis faced interim champion Patchy Mix in a title unification bout on November 17, 2023 at Bellator 301.
[78] Pettis made his MMA debut in Japan on June 9, 2024 as he faced Kyoji Horiguchi in a rematch at RIZIN 47.
Sergio graduated from Pius XI Catholic High School located in Milwaukee, WI in June 2011.
[81] On November 23, 2003, their father, Eugene Pettis, Jr. was stabbed to death by a robber at a friend's house.