He started in radio and moved to SF, publishing in Startling and Thrilling Wonder Stories in 1949. Considering the flowering of the field, it was the perfect time to enter. His first big sale would have been the next year to John W. Campbell's Astounding, the leading SF magazine of the time, and in Amazing, the oldest SF magazine.
Comparatively, it was a strange time to publish SF. Novels were not as common as the magazines, so one could find a home for their stories and later reassemble them into novels. Once the book market opened a lot of writers did that, so that it seemed the best way to make novels (Ray Bradbury's Martian Chronicles, for instance, was sold as a novel, but was really just a collection).
Throughout Gunn's career, this was how he often built novels. He considered the novelette the ideal length for SF, and would publish them first in the magazines, later as a novel. Sometimes the stories were more successful as stories, sometimes as novels. Usually, the first story in the series got him the most attention. Examples:
- "The Cave of Night" opened Station in Space and was reprinted by Judith Merrill and Isaac Asimov as among the best of SF published that year.
- "Child of the Sun" opened Crisis! and was reprinted by Arthur W. Saha and Donald A. Wollheim as among the best of SF published that year.
- "The Listeners" of the novel The Listeners was up for the Nebula award and reprinted by Poul Anderson as among the best of SF published that year. [The novel was the runner-up for the Campbell award]
- "The Giftie" of the novel Gift from the Stars was up for the Sturgeon award and won the Analog reader's poll.
I studied under him several times both online and in person: to learn about SF and stories. When it came to SF, his advice was always wise.
I restarted his online classes, and he tasked me to round up students. To make it happen, I had to use myself twice, once as myself and once as a pseudonym. I divided my artsy self from my science-y self and wrote SF and speculative stories. I varied my critiques, likewise. My critiques for myself, which might seem to be tricky, weren't too hard as they described what I intended to do in the next draft. I pulled off the pseudonym so well, that when I admitted to what I'd done, he didn't believe me. I pointed out that I paid for "both" students, which I think I must have originally explained that "he" didn't have a checking account. Electric Velocipede, a fun little zine sadly no longer in print, published the story under my real name.
I reviewed a number of his works over the years and interviewed James Gunn here.