The 30-year-old becomes the sixth new face at stadium:mk after being released by Watford at the end of last season.
"The coaching staff were very impressed with Stuart during his trial period. He's a very level-headed player with a big presence that will be a good addition to the squad," Dons chairman Pete Winkelman told the club's official website.
"Willy Gueret has been a huge part of our success in the last two years but competition can only be good for him and Stuart's challenge is to provide that."
Searle started his career with non-league Basingstoke before earning a dream move to Chelsea in 2007 where he played in the reserve-team and was a part-time coach at the club's academy. He followed former Blues reserve-team coach Brendan Rodgers to Watford at the start of this year.
Searle, who joins Danny Woodards, Jabo Ibehre, Stephen Gleeson, David McCracken and Jermaine Easter in signing for the Dons this summer, could make his Dons debut in Saturday's pre-season friendly at Windsor and Eton.