The Republic of Ireland Under 21 international midfielder, who has been out on loan at Hereford earlier this year, has joined The Dons on loan for the remainder of the season.
"We're bringing Stephen in to help us in the rush to the end of the season, Dons manager Roberto di Matteo told his club's official website.
"He's a player that can add a lot of quality to our midfield and give us some more strength in that department."