Miller wrote pulp science fiction beginning in the 1930s, and is considered one of the more popular authors of the period. His work appeared in such magazines as Amazing Stories, Astounding, Comet, The Magazine of Fantasy and Science Fiction, Marvel Tales, Science Fiction Digest, Super Science Stories, Unknown, Weird Tales, and Wonder Stories, among others. An active fan of others' work as well as an author, he is also known as an early bibliographer of Robert E. Howard's "Conan" stories in the 1930s, together with his friend John D. Clark.
Clark first encountered Robert E. Howard's fantasies of Kull, Conan and Solomon Kane in the magazine Weird Tales. He became an avid fan, and together with Miller he worked out an outline of Conan's career and a map of the world in Howard's invented Hyborian Age in early 1936 from the then-published stories. Miller sent this material to Howard, whose reply confirmed and corrected their findings. Their map became the basis of those that later appeared in the book editions of the Conan stories. Their revised outline, "A Probable Outline of Conan's Career" was published in the fanzineThe Hyborian Age in 1938. Thus established as an authority on Conan, Clark was invited to edit and provide introductions for the first book editions of Howard's Conan stories, published by Gnome Press in the 1950s. Expanded versions of his and Miller's essay on Conan, retitled "An Informal Biography of Conan the Cimmerian", appeared in the Gnome volume The Coming of Conan in 1953 and in the fanzine Amra, vol. 2, no. 4, in 1959. It was the source of the linking passages between the individual Conan stories in both the Gnome editions and the Lancer paperback editions of the 1960s. Clark and Miller's Hyborian Age map, together with Howard's own original, are the basis of those published in the Gnome, Lancer, and later editions of the stories. Miller gradually shifted into book reviewing beginning in 1945, initially for Astounding Science Fiction and later for its successor, Analog. He began a regularly monthly review column in the former in October, 1951. As a critic he was notable for his enthusiasm for a wide coverage of the science fiction field. He was awarded a special Hugo Award for book reviews in 1963. After his death his sister Mary E. Drake donated his extensive collection of papers, maps, books and periodicals, accumulated largely as a result of his review work, to the Carnegie Museum. They now form the basis of the P. Schuyler Miller Memorial Library at the Edward O'NeillResearch Center in Pittsburgh.