McKenna began his writing career publishing science fiction, and starting in 1958 he regularly attended the annual Milford Writer's Workshop for science fiction writers. "He had enormous talent," writes his colleague Ben Bova in the book "Notes to a Science Fiction Writer". His first science fiction story "Casey Agonistes" immediately established him as a writer to be watched when it appeared in the September 1958 issue of "The Magazine of Fantasy and Science Fiction". Only a handful of his science fiction tales were published during his lifetime, but after his death several more appeared posthumously.