Manly MacDonald was born in 1889 in Point Anne, Ontario. He took classes at the Ontario College of Art in Toronto, then in 1911 traveled to attend the Albright School of Art in Buffalo, New York. From 1912 to 1913 he continued his art studies at the Boston Museum of Fine Arts. He returned to Toronto and from 1914 to 1916 went again to the Ontario College of Art. In 1917 a Royal Canadian Academy of Arts scholarship enabled him to travel to Europe. On his return to Canada, in 1918 the Canadian War Memorials Fund commissioned him to paint scenes of women working in the fields at Quinte, Ontario. In 1920, MacDonald received a second RCA scholarship and traveled to Europe and the United Kingdom. In 1922, he established a studio in Toronto and lived part of the year in Belleville. MacDonald was best known for his depictions of historic southern Ontario - a world of peaceful villages, farms and the people working on them, as well as the surrounding landscape.

MacDonald exhibited in the prestigious Wembley Exhibition in 1924 in England and the British Empire Exhibition in 1925. His work was included in a major exhibition of Canadian art at the Tate Museum in England and in the 1939 exhibition of Canadian art at the New York World's Fair. MacDonald also taught; in 1940 at the Royal Canadian Academy and at the Ontario College of Art from 1943 to 1944 and from 1946 to 1947.
He was a member of the Ontario Society of Artists, an Associate and later, Academician of the Royal Canadian Academy, as well as a founding member of the Ontario Institute of Painters.

His work is in the collections of the Canadian War Museum, the National Gallery of Canada, the Art Gallery of Ontario, the Royal Collection Trust, the John M. Parrott Art Gallery in Belleville, the Loyalist College in Belleville and many others. He died in 1971.