[2] Originally focused on mixed martial arts (MMA), ONE events have since incorporated muaythai, kickboxing, and submission grappling bouts.

It saw Nicole Chua, Singapore's first female professional MMA fighter, submit seven time Indian kickboxing champion Jeet Toshi.

[14] The inaugural ONE Featherweight World Championship followed on 3 February 2013 at ONE FC: Return of Warriors, where Honorio Banario defeated Eric Kelly.

[16] At ONE FC: Rise of the Kingdom on 12 September 2014, Adriano Moraes became the first ONE Flyweight World Champion after submitting Geje Eustaquio.

[17] The ONE Middleweight World Championship was introduced at ONE FC: Battle of the Lions on 7 November 2014, where Igor Svirid defeated Leandro Ataides in 17 seconds for the title.

[22][23][24] The fight showcased Burmese fighters Phyan Thway and Soe Htet Oo in a dark match and the result was a draw according to traditional Lethwei rules.

[27] The inaugural ONE Women's Atomweight World Championship title match saw 19-year-old Angela Lee defeat Mei Yamaguchi to become the first female champion in ONE and one of the youngest ever titleholders in combat sports.

[30][31] Xiong Jing Nan defeated Tiffany Teo at ONE: Kings of Courage on 20 January 2018 to win the inaugural ONE Women's Strawweight World Championship.

[34] On 6 October 2018, ONE: Kingdom of Heroes was headlined by Srisaket Sor Rungvisai defending his World Boxing Council championship against Iran Diaz.

The inaugural ONE Flyweight Kickboxing World Championship match took place at ONE: Warriors of Light on 10 May 2019, where Petchdam Petchyindee Academy defeated Elias Mahmoudi.

[40] 17-year-old Smilla Sundell became the youngest champion in ONE history on 22 April 2022, when she defeated Jackie Buntan at ONE 156 for the inaugural ONE Women's Strawweight Muay Thai World Championship.

[52] Former Strikeforce and UFC Women's Bantamweight Champion Miesha Tate was a vice president of ONE from 2018 until 2021, when she returned to active competition as a fighter.

[65] On 19 September 2019, it was announced that sports streaming service FITE TV would broadcast the promotion's two-part, 100th numbered event, Century.

[68][69] On September 29, 2022, ONE announced an exclusive multi-year partnership with beIN Sports to broadcast live ONE Championship events across the Middle East and North Africa for the first time.

[75] Three judges score the bout in its entirety, not round-by-round, utilizing the following criteria in descending order of importance:[75] Illegal targets for strikes are the groin, throat, trachea, and the back of the head, neck or spine.

[76] Soccer kicks to the head of a grounded opponent were previously legal in the competition, initially via an "open attack" rule, which required fighters to get permission from the referee to use them.

[77] In September 2012, the company adopted the Pride Fighting Championships' rules on the technique, allowing fighters to use soccer kicks without asking for permission from the referee.

The change took place after the death of 21-year-old Chinese fighter, Yang Jian Bing (who was supposed to face Geje Eustaquio) on 11 December 2015, due to dehydration by weight-cutting in the Philippines.

[85] The promotion’s revised policy on weight mandated that athletes are monitored in their training camps, and have urine specific gravity tests to ensure they are hydrated up to three hours ahead of their bouts.

[90] In November 2017, it was announced that ONE VP Rich Franklin would head up a competition called the ONE Warrior Series, searching for up-and-coming martial artists in Asia.

[97] The first ONE event to consist entirely of ONE Super Series contests was ONE Championship: Immortal Triumph in Ho Chi Minh City on 6 September 2019.

The weekly events started with ONE Friday Fights 1 on 20 January 2023, where Nong-O Gaiyanghadao successfully defended his bantamweight Muay Thai title with a TKO of Alaverdi Ramazanov in the third round.

The event finished as the most-watched show in prime time in Thailand, with a 3.9 rating among males 15 years old and over, according to data collected by Nielsen.

Following a legal dispute with his management team, Moraes signed a new contract that saw him making US$100,000 to show and US$100,000 to win, as well as a US$250,000 flat fee as champion and a US$10,000 monthly salary over two years.

This change has made it more difficult to discern the proportion of revenue derived from cash versus non-cash transactions, potentially obscuring the organization's financial health.

ONE Championship also faced organizational challenges, implementing two rounds of layoffs between March and July 2023, affecting 12 to 15 staff members each time.

[146] On December 9, 2020, and January 6, 2021, Bloody Elbow published a two-part article detailing numerous allegations surrounding ONE Championship, mainly mistreatment of former fighters and employees.

Herbert Burns reported being sidelined for years and denied a title shot after leaving Evolve MMA, a gym founded by the promotion's CEO, Chatri Sityodtong.

For instance, Egyptian Top Team fighters have a combined record of 1 win and 22 losses in ONE, raising questions about matchmaking fairness.

"[150] Former two-division ONE world champion Reinier de Ridder further strengthened these allegations, addressing the difficulty of getting fights with ONE during his post-fight press conference at UFC Vegas 100.