Early career Pettis turned pro on September 10, 2011, against Kyle Vivian at Canadian Fighting Championship 7. He won via TKO in the first round. On January 7, 2012, Sergio took on Mike Lindquist at Madtown Throwdown 26. He won via submission in round one. Pettis fought Tom McKenna at LFC 53. He won via first round submission. Pettis then took on Tony Zelinski at NAFC: Unleashed. He won via second-round TKO. Pettis took on Chris Haney at NAFC: Colosseum. He won via unanimous decision. In his next fight, Pettis defeated Jimmy Jones via unanimous decision at RFA 4-Griffin vs Escudero. Pettis was originally set to face Matt Manzanares at Resurrection Fighting Alliance 7, but Manzanares was forced out of the bout due to injury. RFA could not find another opponent for Sergio, therefore the bout was scrapped. Pettis is now set to face Josh Robinson at NAFC: Battleground. Pettis improved his record to an unblemished 7–0 with the unanimous decision victory. Resurrection Fighting Alliance announced that Pettis will take on
UFC vet
Jeff Curran for the inaugural RFA Flyweight Championship at RFA 8 on June 21, 2013, inside the historic The
Rave/Eagles Club Milwaukee, Wisc. 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. He won via KO in the first round to win the RFA flyweight title. Pettis faced James Porter for the NAFC Bantamweight Championship, at NAFC: Battle in the Ballroom on September 28, 2013. Pettis won via first round submission and was subsequently signed by the UFC.
Ultimate Fighting Championship Pettis was expected to make his promotional debut against
Vaughan Lee in a bantamweight bout on November 16, 2013, at
UFC 167. A week before the fight Lee was forced out of the bout due to injury and was replaced by
Will Campuzano. Pettis won the fight via unanimous decision. In his second UFC bout, Pettis faced
Alex Caceres at
UFC on Fox 10 on January 25, 2014. He lost the back-and-forth fight via rear-naked choke submission late in the third round. Despite the loss, Pettis won a
Fight of the Night bonus award for the bout. Pettis faced
Yaotzin Meza on June 7, 2014, at
UFC Fight Night: Henderson vs. Khabilov. He won the fight via unanimous decision. Pettis faced
Matt Hobar on December 6, 2014, at
UFC 181. He won the fight via unanimous decision. The bout also earned Pettis his second
Fight of the Night bonus award. Pettis faced
Ryan Benoit in a flyweight bout on March 14, 2015, at
UFC 185. After winning the first round, Pettis was dropped by left hook and finished off with a flurry of ground and pound from Benoit in the second round. Pettis faced
Chris Cariaso on October 3, 2015, at
UFC 192. He won the fight via unanimous decision. Pettis faced
Chris Kelades on April 23, 2016, at
UFC 197. Pettis won the fight by unanimous decision. Sergio was dominating most of the exchanges and defending takedowns by attacking the neck. He stunned Moraga many times and arguably won all 3 rounds. Pettis called out Jussier Formiga in his post fight interview. Pettis was expected to face
Louis Smolka on October 1, 2016, at
UFC Fight Night 96. 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. Pettis was expected to face
Jussier Formiga on January 15, 2017, at
UFC Fight Night 103. However, Formiga pulled out of the fight in late December and was replaced by
John Moraga. He won the fight via unanimous decision. Pettis was expected to face
Henry Cejudo on May 13, 2017, at
UFC 211. However, on May 10, Cejudo pulled out of the fight with a hand injury and the bout was canceled. Pettis faced
Brandon Moreno on August 5, 2017, in the main event at
UFC Fight Night 114. He won the bout via unanimous decision. A rescheduled fight with Cejudo took place on December 2, 2017, at
UFC 218. Pettis lost the fight by unanimous decision. Pettis faced
Joseph Benavidez on June 9, 2018, at
UFC 225. He won the back-and-forth fight via split decision. Pettis faced
Jussier Formiga on October 6, 2018, at
UFC 229. He lost the fight via unanimous decision After the fight, Pettis' head coach Duke Roufus announced that Sergio is returning to the bantamweight division. Pettis faced
Rob Font in a bantamweight bout, on December 15, 2018, at
UFC on Fox 31. He lost the fight via unanimous decision. Pettis was expected to face
Ricardo Ramos on June 29, 2019, at
UFC on ESPN 3. However, on June 15, 2019, it was reported that Pettis pulled out of the bout due to injury. Pettis was scheduled to face
Alex Perez on September 21, 2019, at
UFC on ESPN+ 17. However, Perez pulled out of the bout on August 26 citing an injury, and he was replaced by
Tyson Nam. Pettis won the fight by unanimous decision. Pettis was scheduled to face
Kai Kara-France on December 14, 2019, at
UFC 245. Later, news surfaced that Pettis fought out his contract with his previous fight with Nam, and is testing free agency.
Bellator MMA On October 24, 2019, it was announced that Pettis signed a multi-fight deal with
Bellator MMA. Pettis made his promotional debut at
Bellator 238 on January 25, 2020, against Alfred Khashakyan. He was victorious via first round technical submission. Pettis faced Ricky Bandejas on July 24 at
Bellator 242. He won the bout via unanimous decision.
Bellator Bantamweight Championship Pettis faced
Juan Archuleta for the
Bellator Bantamweight World Championship at
Bellator 258 on May 7, 2021. Pettis won the bout and the title by unanimous decision. Pettis made his first title defense against former
Bellator Bantamweight Champion Kyoji Horiguchi on December 3, 2021, at
Bellator 272. After losing the first three rounds, Pettis came back to win the fight via knockout in round four. For his second title defense and also the first round bout of the $1 million
Bellator Bantamweight World Grand Prix Tournament, Pettis was scheduled to face
Raufeon Stots on April 23, 2022, at
Bellator 279. However Pettis was forced to pull out of the bout and the Grand Prix after sustaining an injury that required surgery. Pettis defended the
Bellator Bantamweight World Championship against the reigning
Bellator Featherweight World Champion Patrício Pitbull on June 16, 2023, at
Bellator 297. He won the bout via unanimous decision. Pettis faced interim champion
Patchy Mix in a title unification bout on November 17, 2023, at
Bellator 301. He lost the bout and the belt, being submitted in the second round via rear-naked choke.
Rizin Fighting Federation Pettis made his MMA debut in Japan on June 9, 2024, as he faced
Kyoji Horiguchi in a rematch at
RIZIN 47. Pettis lost the bout via unanimous decision.
Professional Fighters League In 2025, Pettis made his debut in the
Professional Fighters League. He faced
Raufeon Stots at
PFL 7 on June 27, 2025. He won the fight via unanimous decision. Pettis faced
Magomed Magomedov at
PFL Champions Series 3, on October 3, 2025. He won the bout via knockout in the second round. Pettis faced Mitch McKee at
PFL Chicago: Pettis vs. McKee, on April 11, 2026. He lost the bout via unanimous decision. == Personal life ==