The youngest of eight children, Gerald Carter was born in Montreal, Quebec, to an Irish Catholic family. His father was a typesetter for The Montreal Star, his brother, Alexander, would become Bishop of Sault-Sainte-Marie, and two of his sisters would become nuns. Carter attended the Collège de Montréal before studying at the Grand Seminary and the Université de Montréal, where he obtained his Licentiate in Theology in 1936. He was ordained to the priesthood by Bishop Alphonse-Emmanuel Deschamps on May 22, 1937.