Forsey was a supporter of Conservative Party led by Arthur Meighen until he went to Balliol College, Oxford on a Rhodes Scholarship during which he was converted to democratic socialism. Upon returning to Canada, he joined the League for Social Reconstruction, and was a delegate at the founding convention of the Cooperative Commonwealth Federation (CCF) in 1933 in Regina.
From 1929 to 1941, Forsey served as a lecturer in economics and political science at McGill University. He also taught Canadian government at Carleton University in Ottawa and Canadian government and Canadian labour history at the University of Waterloo. From 1973 to 1977, he served as chancellor of Trent University.
While he had become a social radical, he remained a "Constitutional conservative", and wrote his PhD thesis on the King-Byng Affair, defending the positions of Arthur Meighen and Governor-General Baron Byng. The thesis was published in 1943 as The Royal Power of Dissolution of Parliament.
Forsey was president of the CCF in Quebec in the 1930s. He spent a number of years working for the CCF, and then as research director for the Canadian Congress of Labour and its successor, the Canadian Labour Congress (CLC). He was a candidate for the party in the Ottawa area riding of Carleton in a 1948 by-election, but lost to the new Progressive Conservative Party of Canada leader George Drew. When asked why he lost he famously quipped that it was because the other candidate received more votes. He ran and lost again in the 1949 election.
In 1958, Forsey, though still a CCF member, was appointed by the government of John George Diefenbaker to the Board of Broadcast Governors, the predecessor of the Canadian Radio-television and Telecommunications Commission. He remained in that position until he resigned in 1962 because of policy differences.
Shortly after the formation of the New Democratic Party from the alliance of the CLC with the CCF, Forsey resigned from the party because of its constitutional policy which viewed Quebec as a nation within Canada. Later in the 1960s, he was attracted to the views of Pierre Trudeau on the Canadian constitution, and joined the Liberal Party of Canada upon being appointed to the Senate in 1970. He retired from the Upper House on reaching the age of 75 in 1979, and turned down an offer from the Liberals to run for a seat in the Canadian House of Commons. He subsequently resigned from the Liberal Party in 1982 due to disagreements with the proposed changes to the Constitution of Canada.
In retirement Forsey published a study of the labour movement in 1982, Trade Unions in Canada: 1812-1902. His publication How Canadians Govern Themselves is perhaps his most enduring legacy, being a simple yet comprehensive guide to Canadian government that is continuously edited and published with posthumous credit.
Works by Forsey
- A life on the fringe : the memoirs of Eugene Forsey. Toronto : Oxford University Press, 1990.
- How Canadians govern themselves, 6th ed. (ISBN 0-662-39689-8) Ottawa : Canada, 2005 (1st ed. 1980, 2nd ed. 1988, 3rd ed. 1990).
- Freedom and order. Toronto : McClelland and Stewart, 1974.
- The royal power of dissolution in the British Commonwealth. Toronto : Oxford University Press, 1938, reprinted 1968.
Works about Forsey
- Hodgetts, J.E. The sound of one voice : Eugene Forsey and his letters to the editor. Toronto : University of Toronto Press, 2000.
- Evatt and Forsey on the reserve powers. Sydney : Legal Books, 1990.
- Political biography from the Library of Parliament
- Order of Canada Citation
- How Canadians Govern Themselves, current edition from Library of Parliament
- Obituary, New York Times