[2] On August 3, 2008, Nong-O fought against Kōji Okuyama at Keio Plaza hotel in Hachiōji, Tokyo, and he won by KO with left elbow strike during 3rd round.
Trijak was the current champion at featherweight sanctioned by the Professional Boxing Association of Thailand, but Nong-O won by majority decision (2-0) after five rounds.
On January 19, 2011, Nong-O Sit Or was named 2010 Boxer of the Year at the Society of Friends of Sportswriters Awards Night in Bangkok.
He then lost a very close fight to Singdam in May, which many thought Nong-O had done enough to win, but beat Petboonchu FA Group in June.
[13] Following a competitive hiatus in which he moved to Singapore to coach at Evolve,[14] Nong-O returned in 2018 when ONE Championship unveiled their new striking format: the ONE Super Series.
Nong-O debuted on April 20 at ONE Championship: Heroes of Honor and defeated Fabio Pinca via unanimous decision.
[15] He returned to his Thai homeland in October at ONE Championship: Kingdom of Heroes, and defeated Mehdi Zatout via unanimous decision.
[16] On February 16, 2019, Nong-O defeated Han Zihao by unanimous decision to become the inaugural ONE Bantamweight Muay Thai World Champion at ONE Championship: Clash of Legends in Bangkok.
[23] Nong-O made his fifth title defense of the ONE Bantamweight Muay Thai World Championship against Felipe Lobo at ONE: X on March 26, 2022.
[25] Nong-O defended his ONE Bantamweight Muay Thai World Championship against Liam Harrison at ONE on Prime Video 1 on August 27, 2022.
[27] Nong-O was scheduled to face former ONE Bantamweight Muay Thai World Champion Alaverdi Ramazanov for his seventh title defense on January 14, 2023, at ONE on Prime Video 6.
[30] Nong-O faced against former ONE Flyweight Muay Thai World champion Jonathan Haggerty for his eighth title defense on April 22, 2023, at ONE Fight Night 9.