Robson, who has not managed a club since February 2007, said he wanted to prove he has what it takes to be a success in the international game and was just waiting for the right job.
"It's not an option to get back to the Premiership, it's an international job I've always quite fancied," he told Reuters in an interview on Friday.
"I decided I wasn't going to drop too far down the league. I've been offered quite a few club jobs around the world and in the (English) Championship, but that wasn't the challenge I needed at the time.
"This is a big challenge, one I'm really looking forward to."
The 52-year-old, who was nicknamed "Captain Marvel" as a player, becomes Thailand's ninth foreign coach since 1976 and the third ex-England international to take the notoriously difficult job after Peter Withe and Peter Reid.
The Thailand job will be Robson's first foray into international coaching after managing English sides Middlesbrough, Bradford City, West Bromwich Albion and Sheffield United.
"I disagree with people who knocked my career as club manager. I wasn't successful at winning a trophy, but to try and do that you need to be with bigger clubs with resources," he said.
"When I look back I was fairly successful as club manager...all the experience I have should help me with this national job."
Robson's first task will be to qualify for the 2011 Asian Cup in Qatar. Thailand are third in Group E with two points from their first two games.
"The Thai squad has good players, youngsters coming through, and I want to work with them to give them confidence and get the best out of them," he said. "I wouldn't have joined if there wasn't a possibility of some success."
"He didn't want me to go, but it's difficult when you've been involved all your life and you don't get to work with players and coaches on the training pitch," Robson said.
"But he un
