Early career After going 2–0 as an amateur, Peña made her professional MMA debut in May 2009. The fight took place just two months and one week after Peña was involved in an accident with a drunk driver while walking in downtown Spokane in which she was knocked unconscious and suffered a broken nose. Ten months later she returned to professional competition in a fight in the flyweight division, a move down from the bantamweight division, losing by unanimous decision.
The Ultimate Fighter In August 2013, it was announced that Peña was one of the fighters selected to be on
The Ultimate Fighter: Team Rousey vs. Team Tate. Peña faced
Gina Mazany in the elimination fight to get into the house. She controlled the fight from early on, winning a clear unanimous decision victory after two rounds. During the first tournament fight in the house, Peña faced veteran and top-ten ranked
Shayna Baszler. Ronda Rousey selected this match-up between the two first female picks. The highly ranked and more experienced Baszler was widely considered the favorite. After a back and forth first round in which Peña landed effective boxing combinations and escaped several of Baszler's submission attempts, Peña came out hard in the second round, connecting with powerful knee strikes that staggered Baszler. The fight went to the ground, where Peña was able to achieve back mount and won via
rear naked choke for perhaps the biggest upset victory of the season. In the semifinals, Peña faced off against Sarah Moras. The two fought previously in a professional bout in 2012, with Peña losing after suffering an injury due to an armbar which forced the doctor to stop the bout between the second and third rounds. Peña won the fight via
guillotine choke in the second round to avenge the loss.
Ultimate Fighting Championship , January 2014 Peña faced
Jessica Rakoczy in the finals on November 30, 2013, at
The Ultimate Fighter 18 Finale. She won the bout via TKO in the final seconds of the first round and became
TUF 18 women's bantamweight champion.
Injury Peña was expected to face
Jessica Andrade at
UFC 171 on March 15, 2014. However, Peña pulled out of the bout after suffering an injury to her right knee. She suffered the injury while grappling in training, ultimately damaging, among other aspects, her
ACL,
MCL,
LCL and
meniscus. Despite the severity of the injury, doctors assured Peña that her right knee would return to full strength following surgery and rehabilitation. The injury kept Peña out of action for the rest of 2014.
UFC return Peña returned to face Milana Dudieva on April 4, 2015, at
UFC Fight Night 63. She won the fight via TKO in the first round. The win also earned Peña her first
Performance of the Night bonus award. Peña next faced
Jessica Eye on October 3, 2015, at
UFC 192. She won the fight by unanimous decision. Peña faced former title challenger
Cat Zingano at
UFC 200 on July 9, 2016. She won the fight by unanimous decision. Peña faced
Valentina Shevchenko at
UFC on Fox 23 on January 28, 2017. She lost the fight via armbar submission in the second round. On October 14, 2017, Peña announced that she was pregnant and would be taking an indefinite hiatus from the sport. On July 13, 2019, at
UFC Fight Night 155, nearly two and a half years from her last bout, she returned and faced former
UFC Women's Flyweight Champion Nicco Montaño, replacing an injured
Sara McMann. She won the fight via unanimous decision. Peña was expected to face
Aspen Ladd on March 28, 2020, at
UFC on ESPN 8. However, Peña pulled out of the fight in early March citing an injury. Peña faced
Germaine de Randamie on October 4, 2020, at
UFC on ESPN: Holm vs. Aldana. She lost the fight via a guillotine choke in round three. Peña was expected to face
Sara McMann on January 16, 2021, at
UFC on ABC 1 before being pushed back a week later to
UFC 257 on January 24, 2021. Peña won the fight via submission in round three. Peña was scheduled to face
Holly Holm on May 8, 2021, at
UFC on ESPN 24. However, Holm was forced to withdraw from the bout citing
hydronephrosis.
Bantamweight champion Peña was expected to face
Amanda Nunes for the
UFC Women's Bantamweight Championship on August 7, 2021, at
UFC 265. However Nunes tested positive for
COVID-19 on July 29, 2021. The bout was rescheduled to
UFC 269 on December 11, 2021. After a dominant round one from Nunes, Peña came back in the second to win the bout and championship by rear-naked choke submission in what is regarded as one of the biggest upsets in UFC history. On February 5, 2022, it was announced that Peña and Nunes would be the coaches for
The Ultimate Fighter 30 on
ESPN+, which would feature contestants from the heavyweight and women's flyweight divisions. A rematch against
Amanda Nunes for the
UFC Women's Bantamweight title took place on July 30, 2022, at
UFC 277. Peña lost the fight by unanimous decision. A trilogy bout with
Amanda Nunes was scheduled to take place on June 10, 2023, at
UFC 289. However, on May 2, 2023, it was announced that Peña pulled out of the bout due to broken ribs she sustained during training camp.
Irene Aldana, who was scheduled to headline
UFC Fight Night: Dern vs. Hill, was subsequently chosen to replace her. Peña faced
Raquel Pennington for the
UFC Women's Bantamweight Championship on October 5, 2024, at
UFC 307. She reclaimed the championship by winning the bout by split decision. 25 out of 26 media outlets scored the bout for Pennington and one scored it as a draw. Peña faced
2019 and
2021 PFL Women's Lightweight Champion (also
2012 and
2016 Olympic gold medalist in judo)
Kayla Harrison on June 7, 2025, at
UFC 316. She lost the championship via a kimura submission at the end of the second round. ==Film and television==