The Scottish actor, who was the seventh Doctor and played Radagast in The Hobbit, will appear in Journey Bound.
The film tells the tale of a young lawyer chasing the love of his life through the Highlands.
McCoy, 70, from Dunoon, will appear in the indie flick alongside Still Game star Ford Kiernan, former Doctor Who star Frazer Hines and Gregory's Girl actress Clare Grogan.
Award-winning cinematographer John Rhodes and musician Gordon Dougall are also working on the film.
Ryan Hendrick, the Bafta-nominated film-maker who's producing Journey Bound, said: "It is fantastic that such esteemed and talented professionals like Ford, Clare, Frazer, John, Gordon and now Sylvester are wanting to be involved in this project as they all understand what we are trying to achieve."
Journey Bound starts filming later this year.