John Ewart (January 31, 1788 – September 18, 1856) was a Canadian architect and businessman.
He built a hospital and then the town's first Roman Catholic church, St. Paul's.
In 1829, he prepared the design for the original Osgoode Hall; some remodelling and additions occurred later.
He continued to operate a building yard and was a director on the boards of several institutions in the city after 1830, although he had retired as an architect.
His daughter, Jane, was wife of Sir Oliver Mowat, and his son, Thomas Ewart, was married to Catherine Seaton Skirving, a noted philanthropist.