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.
Reid left a sour taste in the mouths of Thai fans when he parted company with the team on September 9 after less than a year in charge to become assistant manager at Stoke City.
Robson played in three World Cups and was capped 90 times by England, scoring a staggering 26 goals from midfield. However, Thai fans and soccer columnists have expressed concerns the team has inherited an expensive name rather than a proven coach.
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.
NO FAILURE
He rejected suggestions that his managerial career had been a failure so far and said he planned to prove his critics wrong by helping the Thais, ranked 110th in the world, to climb the FIFA rankings.
"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.
He said he had missed coaching and jumped at the chance to lead Thailand into the Asian Cup finals. He plans to help improve the Thai league and grassroots game to eventually steer the soccer-obsessed nation to its first World Cup finals.
"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."
Robson will continue his role as a global ambassador for Manchester United but said manager Alex Ferguson had expressed disappointment about the move to Asia.
"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
