Jonathan Haggerty (born 18 February 1997) is a British Muay Thai fighter currently signed with ONE Championship. He is the reigning ONE Bantamweight Muay Thai and Kickboxing World Champion and former ONE Flyweight Muay Thai World Champion.
 Haggerty grew up in Walworth Road, London,[citation needed] with a younger brother and two younger sisters. He learned Muay Thai from his father at the age of 7, and he started competing as an amateur at the age of 12. He is a supporter of his local football team Millwall FC.
 Haggerty made his professional debut in 2014, against Anthony Edwards, winning the fight by a fourth round TKO. He would win his next four fights by stoppage, before fighting Gery Bavetta at Muaythai Mayhem for the ISKA World Super-Featherweight Muay Thai title. He defeated Bavetta by a third round knockout.
 In his next two fights, Haggerty defeated Geo Marchese and James O'Connell by a first round stoppage. He suffered his first professional loss during Yokkao 28, losing a decision to Ja Kiatphontip. He rebounded with a second round knockout of Keith McLachlan at Yokkao 29. He was scheduled to fight Liam Harrison at Yokkao 31, but the fight would later fall through. Harrison was replaced by Superlek Kiatmuu9, with Superlek winning by TKO. Before appearing at Yokkao 31, Haggerty won the WBC Muaythai Super Featherweight International title with a TKO of Isaac Araya.
 Haggerty made his ONE Championship debut in January 2019 and defeated Joseph Lasiri via unanimous decision.
 On 4 May 2019 he defeated the legendary Sam-A Gaiyanghadao at ONE Championship: For Honor to claim the ONE Flyweight Muay Thai World Championship.
 Immediately after receiving the belt he called out Thai boxing phenom Rodtang Jitmuangnon against whom he would make his first title defence. The bout took place on 2 August 2019, with Haggerty losing the ONE Flyweight Muay Thai World Championship to Jitmuangnon at ONE Championship: Dawn of Heroes.
 Jonathan Haggerty eventually faced Rodtang in a rematch for the ONE Muay Thai title at ONE Championship: A New Tomorrow on 10 January 2020. He was knocked down in the opening round and was dominated for the remainder of the fight, losing by TKO in the third round after being knocked down three times in the round.
 Haggerty's next fight was against the Japanese opponent Taiki Naito at ONE Championship: Big Bang 2. He won the fight by unanimous decision, scoring a knockdown in both the first and the second round.
 Haggerty was scheduled to face former ONE Flyweight Kickboxing world title challenger Elias Mahmoudi at ONE on TNT 4 on 28 April 2021. Their fight was cancelled due to COVID-19 travel restrictions and Haggerty was unable to make it to the bout. 
 After this Haggerty was due to face Jonno Chipchase on Roar Combat League, though the fight was pulled shortly after. Haggerty faced Arthur Meyer for the ISKA Muay Thai Lightweight World title at Siam Warriors Superfights on 20 November 2021. He won the fight by a second-round knockout.
 Haggerty faced Mongkolpetch Petchyindee Academy at ONE: Bad Blood on 11 February 2022. He won the bout via unanimous decision and was awarded a Performance of the Night bonus.
 Haggerty was booked to face Walter Goncalves in the quarterfinals of the ONE Muay Thai Flyweight Grand Prix at ONE 157 on 20 May 2022. However, close to the fight Haggerty pulled out of the fight citing health reasons and was replaced by Josue Cruz.
 Haggerty was expected to face Amir Naseri in a ONE Muay Thai Flyweight Grand Prix alternate bout at ONE on Prime Video 1 on August 27, 2022. He withdrew from the fight due to a non-COVID related illness on August 24.
 Haggerty revealed that he had been considering a move into MMA with the promotion ahead of his ONE on Prime Video 4 bout, saying "I think that's what they're going to expect me to do like you said, but I feel like the wrestling, the jujitsu, etc, is getting so much better in the UK. You know, people flying abroad to get the work in, and yeah, people are just going to try and take me down, and hopefully, they just walk into a knee.
 Haggerty faced Vladimir Kuzmin on November 19, 2022, at ONE on Prime Video 4. At weigh-ins, Haggerty weigh in at 148 lbs, 3 pounds over the limit. The bout continued at a catchweight and Haggerty being fined 20% of his purse, which went to his opponent Kuzmin. He won the fight via majority decision.
 Haggerty faced Nong-O Gaiyanghadao for the ONE Bantamweight Muay Thai World Championship on April 22, 2023, at ONE Fight Night 9. He won the bout and the title, knocking out Nong-O in the first round.
 Haggerty was scheduled to face the ONE Bantamweight World Champion Fabrício Andrade for the vacant ONE Bantamweight Kickboxing World Championship at ONE Fight Night 15 on October 6, 2023. However, for unknown reasons, the bout was moved to main event at ONE Fight Night 16 on November 4. He won the fight by a second-round knockout.