The Thai superstar announced his decision during a press conference at PK Saenchai Gym in Bangkok on Tuesday (July 21) as he continues his recovery from a broken shin, bringing an end to a reign which began nearly four years ago, reports the Bangkok Post.
“Winning this belt has been a tremendous honour, and that honour will always remain with me, whether or not I have this belt,” Tawanchai said in a statement published on his social media pages.
“I am voluntarily relinquishing the championship out of respect for the organisation and all the fans.”
ONE confirmed that interim champion Nico Carrillo had consequently been elevated to undisputed featherweight Muay Thai champion.
“The division can once again be active,” the Scot said. “You can try, you will not succeed. The belt will be staying with me for a very long time now.”
The promotion said Tawanchai had stepped aside to focus on returning to full fitness while allowing competition in the division to move forward.
The 27-year-old fractured his shin during a kickboxing bout with China’s Liu Mengyang at ONE Friday Fights 137 last December.
A calf kick ended the contest after just 52 seconds, with Tawanchai subsequently undergoing surgery and beginning an extended rehabilitation process.
His injury left him unable to defend the Muay Thai belt he had held since defeating Petchmorakot Petchyindee by unanimous decision in September 2022.
Tawanchai went on to make four successful defences, beating Jamal Yusupov, Jo Nattawut and Superbon Singha Mawynn twice.
His most recent Muay Thai appearance came at ONE 170 in January 2025, when he stopped Superbon in the second round of their rematch.
“Give him the time to prepare, and we’ll see him return stronger than ever. We’ll be waiting for the day Tawanchai shines again,” PK Saenchai gym said in a social media post.
“The belt may not be with him today, but the fighting spirit and the heart of a champion inside Tawanchai have never faded.”
Carrillo’s promotion comes after his coach JP Gallacher publicly called for ONE to strip Tawanchai and elevate the Scottish interim champion.
“We are not waiting for Tawanchai – we are waiting for ONE to do the right thing and strip Tawanchai,” Gallacher told the Bangkok Post earlier this month.
“We and the whole fight scene are asking the same question: why has he not been stripped yet?”
Tawanchai instead chose to relinquish the title voluntarily, removing the need for a unification bout when he eventually returns.
Carrillo, also 27, captured the interim belt with a unanimous decision victory over Shadow Singha Mawynn at ONE Fight Night 40 in February.
The “King of the North” recovered from a difficult opening to take control of their five-round contest, with Shadow suffering a broken jaw during the fight.
Carrillo will nevertheless compete under kickboxing rules in his first appearance since being elevated to undisputed champion.
He faces Chinese newcomer Zhou Jiaqiang at ONE Fight Night 46 at Lumpinee Stadium on August 14, in a temporary switch designed to keep him active.
“We have no plans to stay in kickboxing,” Gallacher said. “This is just a one-time thing to stay busy. Thank you to ONE for the opportunity.”
The identity of Carrillo’s first challenger under Muay Thai rules is less certain.
Luke Lessei stated his case last weekend with a unanimous decision victory over Mohamed Younes Rabah in the ONE Fight Night 45 main event.
The American has made clear that he wants another opportunity against Carrillo, who stopped him in the second round of their first meeting last November.
But the division currently lacks an obvious No 1 contender.
Shadow remains sidelined following his broken jaw, while Bampara Kouyate was forced to withdraw from a scheduled bout at ONE Fight Night 44 after suffering an injury in training.
Jo Nattawut has also retired following his knockout loss last December to Mohammad Siasarani, who could be occupied for the foreseeable future by the featherweight kickboxing tournament beginning next month at ONE Samurai 2 in Tokyo.
ONE may therefore need to blood some of the emerging featherweights building momentum in Muay Thai on its Friday Fights series.
Ireland’s Tom Keogh claimed his third consecutive ONE knockout when he stopped Michael Baranov earlier this month and subsequently warned Carrillo that “his time is coming”.
Turkey’s Ali Kelat has also continued to progress, most recently stopping Elies Abdelali in the third round at The Inner Circle 21.
Both would need to prove themselves against more established opposition before earning a championship fight, but the thinning contender pool could accelerate their rise.
Carrillo now has the undisputed championship his camp demanded. ONE’s next task is finding somebody ready to challenge him for it.