It's a second successive campaign back north of the border for the 28-year-old, who spent 2017-18 with Aberdeen.BCFC
It's a second successive campaign back north of the border for the 28-year-old, who spent 2017-18 with Aberdeen.
The loan will run until 9 June and Blues have the option of a January recall.
Kilmarnock are managed by Steve Clarke and are currently sixth in the table having won, lost and drawn in their three matches so far.
Former Blues winger Chris Burke is part of their side.
Stewart joined Blues from Dundee in August 2016 for an undisclosed sum.
He made 21 league appearances that season, but only started on six occasions.
Last season Harry Redknapp opted to loan him out and the former Rangers wideman linked up with Derek McInnes at Aberdeen.
Stewart, whose Blues contract expires in the summer, was told he would not be figuring in Garry Monk's plans.
Stewart joins Cheick Keita (Eupen), Ronan Hale (Derry City), Cheikh Ndoye (Angers), Nicolai Brock-Madsen (St. Mirren), Jonathan Grounds (Bolton Wanderers), Corey O'Keeffe, Luke Maxwell (both Solihull Moors), Dominic Bernard (Aldershot Town) and Kieron Dawes (Sutton Coldfield Town) out on loan. Leo Brown and Jack Concannon are also at Sutton on a temporary basis.