The Honest men conducted interviews with a number of candidates before selecting the Bullen.
The Pars fans’ favourite played around 130 times for the East End Park side, helping them to the 2004 Scottish Cup Final.
He then moved to Sheffield Wednesday where he captained Paul Sturrock’s side to promotion from League One via the play-offs in 2005.
Bullen, who played in all 11 positions for the Owls, was latterly the club’s under-23s coach and had three spells as caretaker manager.
A statement from Wednesday read: “The native Scot now moves back to his homeland and departs with the sincere thanks and very best wishes of everyone associated with Sheffield Wednesday.”
Ayr, who sit seventh in the Championship, welcome leaders Arbroath to Somerset Park on Saturday.