Founding member 1907 and secretary 1908-9 of the Canadian Art Club and a member of its executive council 1910-15, Williamson brought Dutch subject matter and technique to Toronto in the 1890s. Nicknamed the "Canadian Rembrandt" and known primarily as a portraitist, he painted genre scenes, interiors and landscapes, typically in a dark tonal style developed after more than 10 years of painting in France and Holland following a brief period of study in Paris (1889). He returned to Toronto in 1904 and that year was awarded a silver medal of the St. Louis Universal Exposition. Williamson's later work is more loosely painted and in a higher key. Notable among his portraits is that of Sir Frederick Banting.