Emily Coonan was born in 1885 in the Point St. Charles neighborhood of Montreal. She studied first at the Conseil des arts et manufactures, and later at the Art Association of Montreal art classes, from 1905 to 1912, where prominent teacher William Brymner was an early mentor.

From 1912 to 1913, Coonan traveled to France with fellow artist Mabel May, as well as Holland and Belgium. She was inspired by the French Impressionists, and particularly admired the work of Canadian Impressionist James Wilson Morrice. Her subjects included figurative work drawn from her immediate family and friends, both intimate interiors and outdoor settings, as well asenes. Later, landscape would be her primary focus.

In 1914 Coonan was the first recipient of the National Gallery of Canada Travelling Scholarship. However, due to World War I she delayed her trip until 1921, when she painted for a year in Florence, Venice, Paris and London. In 1916 she won the Special Prize from the Women's Art Society of Montreal. By the 1920s, Coonan was showing Modernist influences, and her work was chosen for exhibition in the British Empire Exhibit in Wembley in 1924.

Coonan was one of members of Montreal's Beaver Hall Group, and kept a studio at 305 Beaver Hall Hill from 1922 to 1924. She did not keep up her ties with the women members after the dissolution of the group as the others did. Between 1908 and 1924, she often showed at the Art Association of Montreal and Royal Canadian Academy annual exhibitions, but her exhibiting career ended with her last appearance at an Art Association of Montreal in 1933. She was a very private person, and stayed close to her family. For the next 30 years, she continued to paint, mostly landscapes, and regularly took sketching trips to the Lower St. Lawrence countryside with her family. She died in 1971 in Montreal. In recent years, there has been a resurgence of interest in her work and that of the other women members of the Beaver Hall Group due to their unique contribution to modernism in Canadian art.