He was born in St-Hyacinthe, Quebec, to a political family. His grandfather, Honoré Mercier and his uncle, Lomer Gouin, were both former Premiers of Quebec. His grandmother's second husband was Liberal Member of Parliament (MP) and later Senator Joseph Godbout. His brother was the judge Gérald Fauteux.
Fauteux married Marguerite Barré daughter of the Canadian artist Raoul Barré (Sept 18th 1923). The couple had 4 children; Roger, Paul, Marie (Mimi) and Gaspard Jr.
A dentist by training and then a businessman, he first entered politics at the provincial election defeating Quebec Conservative Party leader and Mayor of Montreal Camillien Houde to win a seat in the Quebec legislature for the Quebec Liberal Party. He lost his seat in 1935 and returned to business. He was first elected to the House of Commons of Canada from the Quebec riding of St. Mary in a 1942 by-election, and was re-elected in the 1945 federal election by again defeating Camillien Houde. He was re-elected in the 1949 election.
Despite his lack of legal training or long tenure in the House, he was tapped by Prime Minister William Lyon Mackenzie King to become Speaker following the 1945 election.
His inexperience in parliamentary procedure caused him difficulties in the Chair. He had a habit of making decisions before MPs had presented their arguments. He preferred the social aspects of the position and entertained and travelled frequently.
He returned to the backbenches after the 1949 election and, in 1950 was appointed Lieutenant-Governor of Quebec by Governor General Harold Alexander, Earl Alexander of Tunis, on the advice of his prime minister, Louis St. Laurent.