A stair tread overlay includes a tread and a front nosing attached to a front edge of the tread by a tongue and groove joint to provide a strong mechanical joint between the nosing and tread. Adhesive may be applied at the tongue and groove joint to enhance the strength of the joint. A horizontally symmetrical side nosing having a profile matching the profile of the front nosing may be attached an edge of the tread adjacent to the front nosing. The stair tread and nosings may be in the form of a kit used to cover an existing staircase to enhance the appearance of the staircase. The method of making the overlay is also disclosed.