Judo Harrison changed weight classes in 2008, from the 63 kg division to the 78 kg division. She could not compete in the
2008 Summer Olympics as the United States had not
qualified in that division. She won the
2008 Junior World Championship that year, and
the following year placed second, becoming the first American to compete in two
Junior World Championships finals. Harrison won the gold medal in the
78 kg category at the
2010 World Championships, the first American to do so since
1999 (when her coach,
Jimmy Pedro, did so in
Birmingham, United Kingdom). At the
2011 World Championships in Paris, she placed third taking the bronze medal. Harrison had lost to the eventual winner,
Audrey Tcheuméo of France, in her semi-final. Prior to the
2012 Summer Olympics in London, Harrison was injured during training, having torn a
medial collateral ligament. and on August 31, 2016, following her second Olympic gold medal, the
United States Judo Association promoted Harrison to
rokudan (6th Degree Black Belt) making her the youngest person in the US to ever be awarded this rank.
Mixed martial arts Harrison, a former training partner of fellow judoka
Ronda Rousey, announced in October 2016 that she had signed with
World Series of Fighting. While she would initially work as a commentator she also indicated she was contracted to fight, in the women's division.
Professional Fighters League PFL season 2018 Harrison made her MMA debut at
PFL 2 on June 21, 2018, against Brittney Elkin in the Women's Lightweight division. She won via submission due to an armbar in the first round. For her second professional fight, Harrison faced Jozette Cotton at
PFL 6 on August 16, 2018. She won the fight via TKO in the third round. Harrison was on the main card for
PFL 11 in 2018 and defeated Moriel Charneski via first-round TKO; after her victory, it appeared that she was not completely content with her own performance.
PFL season 2019 Harrison was expected to headline the
first event of PFL's second season against Svetlana Khautova on May 9, 2019. Khautova withdrew from the bout and was replaced by
Larissa Pacheco. Harrison won the fight by unanimous decision. Harrison faced Morgan Frier in the co-main event of
PFL 4 on July 11, 2019. She won the fight by key lock submission in the first round. Subsequently, Harrison signed a new long-term contract extension with the PFL. After becoming second in the preliminary round standing, Harrison secured a position at the playoffs. She was originally scheduled to face number 3 ranked Genah Fabian at
PFL 7 on October 11, 2019, but Fabian was forced to pull out of the bout. Fabian was replaced by number 5 Bobbi Jo Dalziel. Harrison would win the fight by an armbar in the first round. Harrison faced
Larissa Pacheco in rematch for the Women's Lightweight final at
PFL 10 on December 31, 2019. After dominating every round with her superior grappling, Harrison won the fight by unanimous decision to win the 2019 Women's Lightweight Championship.
PFL season 2020 Harrison was expected to compete in the season 2020 of PFL, but the complete season was cancelled due to the
COVID-19 pandemic.
Other promotions With the 2020 PFL season cancelled, Harrison was handed a contract exemption to sign with the
Invicta FC and made her debut in the Featherweight division against Courtney King at
Invicta FC 43 on November 20, 2020. She won the fight via TKO in the second round. Harrison was then expected to compete for
Titan FC. She was scheduled to face Jozette Cotton in a rematch on December 17, 2020, at Titan FC 66. The day before the fight, Cotton was hospitalized due to a bad weight cut and the bout was cancelled.
PFL season 2021 Kayla faced
Mariana Morais on May 6, 2021, at
PFL 3 for the start of the 2021 season. She won the bout via TKO in the first round. Kayla faced
Cindy Dandois on June 25, 2021, at
PFL 6. She won the bout in the first round via an arm bar submission. Kayla faced
Genah Fabian in the Semifinals of the Women's Lightweight tournament on August 19, 2021, at
PFL 8. She won the bout in the first round via TKO by way of ground and pound. Kayla faced Taylor Guardado in the Finals of the
Women's Lightweight tournament on October 27, 2021, at
PFL 10. She won the bout via armbar in the second round.
PFL season 2022 Being one of the most sought-after free agents in the sport, Harrison ended up signing a contract with
Bellator MMA in March 2022. However, PFL exercised their matching right, and Harrison re-signed – a deal set to be terminated in December 2023 – with them. She won the bout via unanimous decision. Harrison was scheduled to face
Julia Budd on July 1, 2022, at
PFL 6. However, a week before the event, Budd pulled out due to injury and was replaced by
Kaitlin Young. Harrison won the bout, with the referee stoppage at the 2:35 mark of the first round. Harrison faced Martina Jindrová in the Semifinals off the Women's Lightweight tournament on August 20, 2022, at
PFL 9. She won the bout in the first round via arm-triangle choke. Harrison faced
Larissa Pacheco for a third time in the finals of the
Women's Lightweight tournament on November 25, 2022, at
PFL 10. In an upset, she lost the fight via unanimous decision.
PFL season 2023 After a year hiatus, Harrison was scheduled to face
Julia Budd at
PFL 10 on November 24, 2023. However, Budd was removed from the fight that she "refused to fulfill her contractual obligation" and was replaced by
Aspen Ladd at a catchweight of 150 pounds. Harrison won the fight by unanimous decision.
Ultimate Fighting Championship On January 23, 2024,
Dana White announced that the
UFC had signed Harrison and that she would make her promotional debut, as well as her bantamweight debut, against former
UFC Women's Bantamweight Champion Holly Holm on April 13, 2024, at
UFC 300. Harrison won the fight against Holm by a rear-naked choke submission in the second round. Harrison faced
Ketlen Vieira on October 5, 2024 at
UFC 307. She won the fight by unanimous decision.
UFC Bantamweight Champion Harrison competed for the
UFC Women's Bantamweight Championship against two-time champion (also
The Ultimate Fighter 18 Tournament Winner)
Julianna Peña on June 7, 2025 at
UFC 316. She won the championship via
kimura at the end of the second round. This fight earned her a
Performance of the Night award. Immediately following the victory,
Amanda Nunes entered the octagon to face-off with Harrison. Harrison was scheduled to defend her title against former two-time champion
Amanda Nunes on January 24, 2026 at
UFC 324. However, Harrison withdrew from the bout after being diagnosed with herniated discs in her neck, which required surgery. The fight is expected to be rescheduled for a later date. ==Personal life==