Early life and SF fandom
Weisinger was born in the Washington Heights section of New York City, New York and was raised in the Bronx, as the son of Austrian Jewish parents. His father was a businessman in the garment trade. At 13, he was introduced to science fiction by means of a borrowed copy of the August 1928 issue of Amazing Stories (featuring Buck Rogers and The Skylark of Space). By 1930, Weisinger was active in some of the earliest SF fan clubs and fanzines, including The Planet. In 1931, Weisinger hosted a meeting of pioneer SF fan club "The Scienceers," which was attended by a young Julius Schwartz, who recalled that the two became "very friendly... [and] got along well together." A year later, Weisinger, Schwartz and Allen Glasser joined fellow-future professional editor Forrest J. Ackerman in founding The Time Traveller, which they styled "Science Fiction's Only Fan Magazine". The claim was more than mere youthful bravado, according to SF historian Sam Moskowitz, who described the 'zine as the first devoted entirely to science fiction. Drawing on information they had gleaned from writing letters to the SF magazines and authors of the day, the young fans published interviews with, and short pieces by, established SF writers, and in the process gained increasing familiarity with the personalities and situations of the genre in that era. The first issue featured "a one-page biography of Edward 'Doc' Smith... [and] some news items."
After high school, Weisinger attended New York University, where he worked as editor of the college's newspaper and magazine, but left before graduating. With Schwartz, he approached the editor of Amazing Stories (T. Connor Sloane) and "sold his first story": 'The Price of Peace'. In late 1934, Weisinger suggested that he and Schwartz "ought to go into the agency business," noting (according to Schwartz) that the duo had
||"...got to know a lot of writers and artists and so on... [Mort explained] 'When a writer writes a story he lives out of town, and he mails it to Amazing Stories. If it's rejected, it has to go all the way back to California. So he sends it to Wonder Stories. Then it goes back and forth, because they send it blind. They don't know what the editor wants. Now we talk to the editors, and he can find out if they want an interplanetary story of about six thousand words, or if they want this or that. Then we can relay this information to the writers. And of course we can become their agents and collect the usual fee of 10%.' "
Schwartz concurred, and they formed the Solar Sales Service ("We always believed in alliteration," noted Schwartz), the first literary agency to specialize in the related genres of SF, horror, and fantasy. Edmond Hamilton was the agency's first client, and Otto Binder soon followed. Solar Sales eventually represented many prominent SF and fantasy writers, including John Russell Fearn, Alfred Bester, Stanley Weinbaum, H. P. Lovecraft, and Ray Bradbury. But while Schwartz continued the agency into the early 1940s, Weisinger moved on; he took a job with the Standard Magazine chain, publisher of a range of pulp magazines. Standard had acquired writer-publisher Hugo Gernsback's defunct Wonder Stories and added it to Standard series of "Thrilling" publications (Thrilling Detective, Thrilling Western, and others). Weisinger became the editor of Thrilling Wonder Stories, and bought stories by Hamilton and others from his former partner Schwartz. Weisinger was soon editing a range of other pulps by Standard, including Startling Stories and Captain Future, and "was in charge of no fewer than 40 titles" by 1940.