The ex-Hull City striker makes a move to Buriram United as a free agent on a record-breaking €47,000 (£39,000) per-month contract
Simpson has penned a two-year contract with the option of a further year worth a reported €47,000 a month, making him the highest paid player of all time in the TPL.
The 24-year-old striker was reportedly targeted by the likes of Turkish side Gaziantepspor after he was released by Hull City in the summer, but has opted to join the Thai outfit currently coached by former Real Madrid assistant Alejandro Menendez.
A product of the Arsenal youth academy, Simpson became the first person to score a hat-trick at the Emirates Stadium in a 3-2 FA Youth Cup win over Cardiff in 2007.
He spent time at Millwall and QPR prior to his move to Hull in 2010, where the former England youth international scored 13 goals in 85 appearances before he was released in May this year.