The window over the altar was installed in 1840, the oldest stained glass window west of Quebec. The symbols at the top reflect the attachment of the parish to the Anglican Communion and to the Crown of Great Britain. The lower parts bear ecclesiastical and Masonic symbols.
Seven of the side windows are the work of the McCausland Company of Toronto. The first of these to be installed, the resurrection window, is of particular note.
The two windows in the south transept are from the Lyons Company, later taken over by McCausland. It is likely that the East window was also created by them.
The rear window on the south side of the nave is the only one designed specifically for St. Mark’s. It is the work of Yvonne Williams.