The former Arsenal trainee, who has one England cap, impressed while on trial at the Thai Premier League side and has signed a two-year contract
Bothroyd, who has one England cap, impressed head coach Scott Cooper and his staff while on trial at the Thai Premier League side and has penned a two-year contract. The Mirror reported that the deal is worth £5 million.
Cooper, who personally flew out to scout the 31-year-old when he was on loan at Championship Sheffield Wednesday from Queens Park Rangers (QPR) earlier this year, is delighted with his new signing.
"He's a big figure with technique and pace," he said. "During our latest warm-up match, he adapted well. This is a crucial piece of our victory jigsaw."
Bothroyd himself claimed to have chosen to play in Asia for the first time in his career, despite interest back in England.
"First of all I want to say thanks to SCG Muangthong United for believing in me," he said at his unveiling, where he was assigned the number nine shirt.
"Last week was one of the most challenging moments in my life. Many English teams showed interest in me, from the Premier League to the Championship. Also, there was some interest from the Chinese Super League and Korean K-League Classic, but ultimately I choose Muangthong as they're one of the most successful clubs in Thailand.
"They seriously challenge for every trophy every year with their great squad and they impressed me a lot."
Muangthong general manager Ronnarit Suevaja described Bothroyd's signing as a "big deal" for the club, who finished second in the TPL last season and will take part in the AFC Champions League play-offs for 2014.
"Obviously this is a big deal for us as he is experienced in European top leagues," he pointed out.
"He'll be our ambassador for upcoming activities too. He got some better deals from the likes of Hull City and Cardiff, but I asked, 'Do you still want to play for the title?' If that's what you want, our offer will put you on that track again'.
"It took us from 8p.m to 5 a.m to close this deal - a difficult one indeed!"
Released by QPR in June last year, Bothroyd started his career at Arsenal as a trainee before moving on play in the Premier League with Coventry City, Charlton Athletic and Stoke City. He also had spells in the Championship with Wolverhampton Wanderers and Cardiff City, as well as a stint in Italy with Serie A side Perugia.