Allgood joins Inghinidhe na hÉireann (“Daughters of Ireland”), where she first begins to study drama under the direction of Maud Gonne and William Fay. She begins her acting career at the Abbey Theatre and is in the opening of the Irish National Theatre Society. Her first big role is in December 1904 at the opening of Lady Gregory‘s Spreading the News. By 1905 she is a full-time actress, touring England and North America.
In 1915 Allgood is cast as the lead in Peg o’ My Heart which tours Australia and New Zealand in 1916. She marries her leading man, Gerald Henson, in September 1916 in Melbourne, however, her happiness is short lived. She gives birth to a daughter named Mary in January 1918, who dies just a day later. Her husband dies of influenza during an outbreak in November 1918. After her return to Ireland she continues to perform at the Abbey Theatre. Her most memorable performance is in Seán O’Casey‘s Juno and the Paycock in 1923. She wins acclaim in London when she plays Bessie Burgess in O’Casey’s The Plough and the Stars in 1926.
Allgood is frequently featured in early Alfred Hitchcock films, such as Blackmail (1929), Juno and the Paycock (1930), and Sabotage (1936). She also has a significant role in Storm in a Teacup (1937).
After many successful theatre tours in the United States, she settles in Hollywood in 1940 to pursue an acting career. She is nominated for the Academy Award for Best Supporting Actress for her role as Beth Morgan in the 1941 film How Green Was My Valley. She also has memorable roles in the 1941 retelling of Dr. Jekyll and Mr. Hyde, It Happened in Flatbush (1942), Jane Eyre (1943), The Lodger (1944), The Keys of the Kingdom (1944), The Spiral Staircase (1946), The Fabulous Dorseys (1947), and the original Cheaper by the Dozen (1950).
(Note: Many accounts give October 31, 1879 as her date of birth. Her headstone also gives 1879 as her year of birth. However, her sister Margaret is born on August 1, 1879, meaning she could not have been born in that year. Sara Allgood may have been born on October 31, 1880 but her parents may have been late registering her.)