The 28-year-old former Stevenage, Gillingham and Barnet defender becomes the club's second signing of the summer having closely followed winger Chris Arthur through the door.
"I have heard a lot of good things about AFC Wimbledon because I am best friends with (former Dons striker) Danny Kedwell," Fuller told the club's official website.
"Everybody knows about how the club has come through the leagues and I want to play a part in helping Wimbledon take another step. Danny spoke so highly about the club, including how good the fans are and the atmosphere around the place."
Manager Neal Ardley added: "We were really surprised when Barry became available.
"We liked him when we first played against Barnet last season because he caused us problems. We talked about him afterwards and said that he was the sort of character and player that we wanted at this club.
"When he became available we were delighted and we quickly jumped at the chance to meet with Barry and his Dad on Friday."