The present church building of St. Mark's takes the traditional form of a cross. It contains a wealth of memorial inscriptions that reflect the history of the Niagara-on-the-Lake area.

The windows provide an overview of style and design of glass, spanning a century and a half.

While the building is one of historic interest, it is primarily the place of worship for the Anglican parish of Niagara-on-the-Lake. Over the past two centuries, its shape has been modified and additions made to its furnishings to meet the changing needs of this active parish. During the winter of 2004, the parish hall was renovated and renamed "Addison Hall.