The League One play-off chasers have now received international clearance for the former Arsenal midfielder and he will be included in the squad for the first time on Saturday when Peterborough visit stadium:mk.
Randall, who was recently playing in Italy with Ascoli, last week agreed a short-term contract until the end of the season with his hometown club having spent the past month training with the Dons.
Milton Keynes manager Karl Robinson is excited about the qualities the 24-year-old will add to his squad.
"It's taken longer to get over the line than we would have liked but now I'm now looking forward to having Mark available to select," Robinson told the club's official website.
"He's from MK, he's a talented footballer and he suits our style.
"The first two weeks he trained with the youth team and I'd like to thank Mike (Dove) for his help with that. He then stepped up a grade into the first team and he's done well.
"We're low on numbers and it's a chance for him to rekindle his career, just the same as Ryan Hall."
Randall began his career as a schoolboy at Arsenal but, despite his obvious promise, was never able to hold down a regular first-team spot in Arsene Wenger's side.
He undertook loan spells at Burnley, MK Dons and Rotherham during his time with the Gunners before leaving the Premier League club in 2011 when he joined Chesterfield.
After two years with the Spireites, he signed for Ascoli in the Italian third tier in September 2013 but the club went bankrupt, leaving Randall as a free agent.