A high school dropout, he nevertheless began a career as a freelance writer before World War I.
He was two months short of his 20th birthday when his first story, "The Foreigner", appeared in the May 1916 issue of H. L. Mencken's literary magazine The Smart Set.
[1] During World War I, Leinster served with the Committee of Public Information and the United States Army (1917–1918).
Leinster's 1945 novella "First Contact" is also credited as one of the first (if not the first) instances of a universal translator in science fiction.
[3] In 2000, Leinster's heirs sued Paramount Pictures over the film Star Trek: First Contact, claiming that it infringed their trademark in the term.
Leinster was also an inventor under his real name of William F. Jenkins, best known for the front projection process used in special effects.
[7] He appeared in September 1953 on an episode of the educational series American Inventory, in which he discussed the possibility of space travel.