The 20-year-old, who recently featured for the England team at the World Under-20 Championships in Colombia, spent last season on loan at Bournemouth, having previously gained league experience at Wycombe and Torquay.
MK Dons manager Karl Robinson told the club's official website: "Adam is a young full-back who adds strength and quality to our side.
"He has already proven he can cope at this level and possibly should be even playing in the Championship.
"We're very fortunate to have acquired his services because a lot of clubs were looking at him."
Source: Team Talk
Source: Team Talk