Fowler, who had been playing for Muang Thong, takes over from Henrique Calisto after the Portuguese was axed this week following the club's AFC Cup exit at the quarter-final stage.
"Robbie will be caretaker coach until the end of the season. If he is successful, we may offer him a long-term contract," Ronnarit Suewaja, general manager of Muang Thong, told the ASEAN Football Federation's official website.
"We have to move forward and I am sure that everyone involved will support him. Our target is still the same - we must try to defend the title."
Fowler becomes the fifth coach of Muang Thong in five years, and has been immediately tasked with reviving his side's title hopes - they currently trail Thai Premier League leaders Buriram PEA by twelve points.