Marion Long studied at the Ontario College of Art, in New York at the Art Students League, and in Provincetown. She opened a studio in Toronto in 1913. In 1922 she was elected to the Royal Canadian Academy (Associate) and in 1933 she became the second woman to be elected to the Academy as a full Academician. She was a member of the Ontario Society of Artists (1916), the Ontario Institute of Painters, and she was a member of the Heliconian Club, of which she was the president in 1919. She was commissioned to paint many well-known Canadian men and women, including a series of seven portraits of men and women of the Canadian armed forces in World War II, now in the John Deutsch University Centre of Queenâ€™s University, Kingston. She was also commissioned to do portraits of the Royal Norwegian Air Force and received the King Haakon VII medal of liberation for services to Norway during World War II. In 1943 she was commissioned by Imperial Tobacco to paint eleven portraits of sailors and other servicemen for a Players Navy Cut campaign. She exhibited with the Ontario Society of Artists after 1905, and the Royal Canadian Academy after 1905, at the Canadian National Exhibition, the Art Association of Montreal, Wembley, and the National Gallery 1926. She is represented at the National Gallery of Canada, the Art Gallery of Ontario, the University of Toronto, Annesley Hall, Queenâ€™s University, Art Gallery of Hamilton and in many private collections.