The former Morton, Airdrie, Falkirk, Dundee United and Queen of the South boss was previously in charge of the Jags between 2007 and 2011.
McCall returns to the Energy Check Stadium at Firhill after leaving Championship rivals Ayr United and will be assisted by Alan Archibald and Neil Scally. The first match in charge for the new management team is away to Celtic in the Betfred Cup quarter-final on Wednesday.
Meanwhile, Sandy Stewart takes over on an interim basis at Somerset Park, with Ayr expecting to have a new manager in place by October 21.
