Born near Saint John, New Brunswick, he began his career by studying at the New England Conservatory of Music in Boston. He was a classicaly trained baritone. After working as an actor on stage for a few years, he made his Broadway debut in 1925. He made several silent movies in the 1920s, followed by some early talkie musicals. Afterwards Pidgeon played secondary roles to the main male star in such films as Saratoga and The Girl of the Golden West. It wasn't until he starred in How Green Was My Valley that he became well known.

He starred opposite Greer Garson in Blossoms in the Dust and in Mrs. Miniver (for which he was nominated for the Academy Award for Best Actor). He was nominated again in 1944 for Madame Curie. Although he continued making films, Pidgeon returned to work on Broadway in the mid-1950s after a twenty-year absence. In 1962, he starred in Walt Disney's Big Red, a boy-dog tearjerker. His role as Florenz Ziegfield in Funny Girl (1965) was well received.

He retired fully in 1970, and died in Santa Monica, California, in 1984. In accordance with his wishes, his body was donated to the UCLA Medical School for medical research.

Pidgeon has a star on the Hollywood Walk of Fame at 6414 Hollywood Blvd.