Born into an Irish Protestant family in Portobello, Dublin, Shields started acting in the Abbey Theatre when he was 17 years old.

[1] In 1936, John Ford brought him to the United States to act in a film version of The Plough and the Stars, and in 1939 Shields decided to live permanently in California, where the mild climate would help his tuberculosis.

Shields portrayed the Reverend Playfair in Ford's The Quiet Man, opposite John Wayne, Maureen O'Hara and his brother, Barry Fitzgerald.

[citation needed] He also made television appearances including a 1958 role on Perry Mason as Dr. George Barnes in "The Case of the Screaming Woman" as well as a 1960 episode of Maverick starring Roger Moore titled "The Bold Fenian Men."

His body was cremated, with the ashes taken to his native city of Dublin[1] and buried with military honours in Deans Grange Cemetery.