[4] In early 1914, whilst working in the City he voluntarily enlisted in the British Army's Territorial Force as an infantry soldier with the Honourable Artillery Company as its Private #852.

[5] On 5 January 1915, whilst in trenches at Kemmel in Belgium, he was machine-gunned in the legs, causing multiple wounds and a fractured right thigh, and was subsequently medically evacuated to the United Kingdom, where he spent the rest of 1915 recovering in hospital.

In October of that year, he went to Canada as stage manager to Henry V. Esmond and Eva Moore, also playing "Montague Jordan" in Eliza Comes to Stay.

He returned to Broadway several times during the 1930s, portraying Philip Downes in Ronald Jeans's Lean Harvest (1931), Mr. Jelliwell in Benn W. Levy's Springtime for Henry (1931–1932), His Excellency, Governor of the Colony in Arthur Schwartz's Virginia (1937),[7] and W. S. Gilbert in Oscar Hammerstein II's Knights of Song (1938).

In 1934, he had moved to Hollywood, U.S. As his career there became a success, he set up a home at 701 North Alpine Drive, Beverly Hills in the latter half of the 1930s.

[9]) Loren D. Estleman wrote of Bruce: If a mop bucket appeared in a scene, his foot would be inside it, and if by some sardonic twist of fate and the whim of director Roy William Neill he managed to stumble upon an important clue, he could be depended upon to blow his nose on it and throw it away.

The historian David Parkinson wrote that Bruce's "avuncular presence provided the perfect counterbalance to Rathbone's briskly omniscient sleuth".

Since then, most major modern adaptations of Arthur Conan Doyle's Sherlock Holmes stories, especially since the 1970s, have consciously defied the popular stereotype, and depicted Watson faithfully as a capable man of action.

[16] In 1947 he began writing an autobiography entitled Games, Gossip and Greasepaint, which is unpublished; however, excerpts have been printed in the Sherlock Holmes Journal, and these have been posted online with permission.