The Dublin-born stopper was substituted in the first half of the 3-0 victory over Exeter five weeks ago with a hamstring tear, with Clayton Ince taking over between the sticks for the past four games and loan stopper Mark Oxley coming in as a replacement.
Gilmartin’s return brings with it a selection poser for manager Chris Hutchings but he is likely to keep faith with Ince, with Gilmartin replacing Oxley on the bench.
Mark Bradley will also return in time to take his place in midfield having featured for Wales Under-21s in their 2-1 defeat to Bosnia-Herzegovina on Wednesday.
Full-back Jamie Vincent (calf) and the versatile Richard Taundry (hamstring) will again miss out but both are expected to return to training next week.
The trip to Griffin Park is followed by an FA Cup clash against the Bees seven days later.