Filming began in Edinburgh and Glasgow, Scotland earlier this month.
The project, co-produced by DNA Films and Black Camel Pictures, is being led by director Dexter Fletcher (Wild Bill). Stephen Greenhorn, the man behind the musical, also adapted the film's script.
Sunshine On Leith tells the story of two army veterans returning home from war in Afghanistan; one finds his soul mate, while the other loses the girl he left behind.
The film's name is taken from The Proclaimers' second album.
Also starring with Thomas will be Peter Mullan, Jane Horrocks, George McKay, Kevin Guthrie, and Freya Mavor.
Thomas is best known for her role as Alisha on TV's Misfits, and most recently starred in ITV's military drama, Homefront.