Carroll was born in Weedon Bec, Northamptonshire, to William and Catherine Carroll. His Roman Catholic parents named him after then-Pope Leo XIII. In 1897, his family lived in York, where his Irish-born father was a foreman in an ordnance store. In the 1901 Census for West Ham, Essex, his occupation is listed as "wine trade clerk". In the 1911 census, he is living at the same address and described as a "dramatic agent".
Carroll made his stage debut in 1912. His acting career was on hold during the First World War, when he served in the British Army. He then perfo...