Leslie worked as a journalist for the Sudbury Star and other newspapers in Northern Ontario before briefly moving to the United States in the mid-1920s. There he came in contact with the Stratemeyer Syndicate. Returning to Canada, McFarlane began to write for the Syndicate's Dave Fearless series in 1926, writing seven books under the name of Roy Rockwood. Later the same year, he wrote the first book of the Hardy Boys series, again for the Syndicate, under the pseudonym Franklin W. Dixon. McFarlane wrote over twenty books for the series during the next twenty years. He also wrote the first three books of the Dana Girls series for the Syndicate, written under the name Carolyn Keene, in 1933. While writing these juvenile books, he wrote two novels and scores of short stories and novelettes for pulp and other magazines, including Maclean's, for whom McFarlane became an editor in the 1930s. He then wrote plays for CBC Radio's Canadian Theatre of the Air between 1938 and 1943. In 1943, he joined the National Film Board of Canada as a documentary film writer and director. He also wrote speeches for the Minister of Munitions and Supply during the Second World War. In the 1950s, he wrote television plays for the CBC, becoming head of the television drama script department in 1958. He later returned to writing children's books, including the successful McGonigle Scores!, in 1966. His autobiography, Ghost of the Hardy Boys, was published in 1976. McFarlane and his first wife Amy Arnold had three children: Patricia, Brian, and Norah. Amy died in 1955, and he later married Bea Kenney. Leslie McFarlane died on 6 September 1977 in Whitby, Ontario.