Jim Mooney was born in New York City and raised in Los Angeles. Friends with pulp-fiction author Henry Kuttner and Californian science-fiction fans such as Forrest J. Ackerman, he drew the cover for the first issue of "Imagination", an Ackerman fanzine that included Ray Bradbury's first published story, "Hollerbochen's Dilemma". Kuttner encouraged the teenaged Mooney to submit art to Farnsworth Wright, the editor of the pulp magazine for which Kuttner was writing, "Weird Tales". Mooney's first professional sale was an illustration for one of Kuttner's stories in that magazine. During this period, Mooney also met future comic-book editors Mort Weisinger and Julius Schwartz, who had come to the area to meet Kuttner.