Dorion was called to the bar in 1927 and was the founding president of the Jeune Barreau de Québec in 1934. He was the crown attorney who prosecuted Wilbert Coffin in 1954. The "Coffin affair", as it became known, was a contributing factor in the decision to abolish the death penalty in Canada as it became a widespread belief that Coffin was wrongly convicted and executed.
Dorion entered politics in the 1945 federal election, running as an Independent in Quebec East, but was unsuccessful. Dorion finished in second place behind Louis St. Laurent, and was the unofficial Conservative standard-bearer as the riding had no official Tory candidate. He ran as an independent along with his brother Frédéric Dorion, an incumbent MP, due to his opposition to conscription in the Conscription Crisis of 1944.
Dorion was appointed to the Canadian Cabinet in 1960 as Secretary of State for Canada, and was reassigned to the position of President of the Queen's Privy Council for Canada in 1961. He held this position until his defeat in the 1962 federal election. Dorion returned to his law practice and remained an active lawyer until his death.
- Law Society of Quebec biographies (in French)