Thanakarnjanasuth, also known as 'Tiger', held a 25% stake in Championship club Reading until May 2017 as part of a three-person consortium.
The takeover ends Darryl Eales's tenure as chairman of the U's, although he retains a shareholding and significant investment in the club and will remain on the board.
"My ambition has always been to help the club achieve sustainable success," Eales told the club's official website.
"We have made significant progress on and off the pitch, and I believe a partner with similar ambition but greater resources will accelerate the prospect of achieving this objective.
"Tiger has the financial resources, high level connections in football, including with the EFL, and, critically, the passion and drive which can deliver on the club's ambitions. We have formed a good relationship and I am delighted to welcome him to the club."