He studied at Harvard until the First World War broke out in 1914. At that point, aged 23, he returned to Canada and joined the Canadian army in Halifax and was assigned to the Cyclist Corps of the Second Division, Canadian Expeditionary Force. In March, 1915, he asked for and got a discharge, and on April 3 enlisted in the First Newfoundland regiment which was about to cross the Atlantic and join up with the British army.
In 1915, although most of the soldiers in his regiment were transferred to Aldershot in order to be sent on to Malta, Gallishaw was dispatched to London in order to undertake office work. On the eve of his dispatchment, he took advantage of an order to board a train bound for the embarkation port for Malta. During the journey, he complained to an adjutant who assigned him to B company of the regiment. He took part in the evacuation of Gallipoli where he was wounded and eventually he was demobilised.
He returned to Harvard but this time as a lecturer. In 1917 the United States joined the war and he enlisted again, this time in the American army. He was sent to France where he took part in several battles. By force of circumstances he became commander of a battalion, joined the United States American Army Intelligence Service and served as a liaison officer with the British forces.
Galllishaw published five books. The first, Trenching at Gallipoli is subtitled A Personal Narrative of a Newfoundlander with the Ill-fated Dardanelles Expedition and was dedicated to Professor Charles Townshend Copeland. His second book, The Man in the Ranks is the tale of a soldier and was written in collaboration with William Lynch.
His three remaining works discussed the writing of books:
- The Only Two Ways to Write a Story,
- Twenty Problems of the Fiction Writer, a series of short essays on techniques for the writing of short stories.
- Advanced Problems of the Fiction Writer, an essay on the form of plots.
Of these only the first was still in print in 1982.
In addition to these books he published literary analyses and criticism, as well as setting up the John Gallishaw School of Creative Writing in Cambridge, the town where Harvard is situated. He wrote material for the theatre, radio and television. He worked in Hollywood as a scriptwriter for Metro-Goldwyn-Mayer (MGM), Columbia Pictures, Paramount and Universal Studios. He worked with Francis Scott Fitzgerald and became friendly with Clark Gable, Robert Young, Cary Grant, Jeanette MacDonald and Nelson Eddy. During this period he also presented courses at the University of California and at the University of Hawaii.
In 1961 he returned to St. John's for the official opening of the Memorial University of Newfoundland. He died in 1968.
- Trenching at Gallipoli. A Personal Narrative of a Newfoundlander with the Ill-fated Dardanelles Expedition (1916)
- The Man in the Ranks (1917)
- The Only Two Ways to Write a Story (1928)
- Twenty Problems of the Fiction Writer (1929)
- Advanced Problems of the Fiction Writer (1931)
- Biography from Encyclopedia of Newfoundland and Labrador, Volume 2, Joseph Smallwood, Catherine Horan, Robert Pitt, Betram Riggs, editors, Newfoundland Book Publishers, St. John's, Newfoundland, 1984, pages 463-464
- Alonzo John Gallishaw's biography