Mary Eastlake was born in Douglas, Ontario in 1864. She studied in Montréal with Robert Harris, in New York at the Art Students League with William Chase in 1885, and at the Académie Colarossi.
She worked with oil and pastels, her subject matter often landscapes and portraits, especially including children.
In 1886 she was commissioned to paint a number of works for American patrons in New York. She traveled to France and England in 1890 and to Paris in 1891.
She became a member of the staff of Victoria School of Art, Montréal, in 1892.
In the early 1890's she lived briefly in Almonte, Ontario. She later moved to England and settled in St. Ives, where she met and married the English painter Charles H. Eastlake. Wither her husband, they created jewelley enamels.
Throughout her life she traveled extensively in Europe and Asia. In 1939 the couple returned to Montréal and then Almonte, Ontario.
She became a member of the Royal Canadian Academy in 1893 but resigned following her marriage. She was also a member of the Pastel Society of London, The Women’s International Art Club, and the Boston Water-Colour Society.
She exhibited with the Art Association of Montreal from 1888-1943, with the Ontario Society of Artists in 1892, The Royal Canadian Academy from 1887-1943, The Toronto Industrial Exhibition in 1894, The Royal Institute of Painters in Oil, The London Pastel Society and also in Buffalo, Boston among others.
She died in Ottawa, Ontario in 1951.