Palmer rose through the ranks of science fiction fandom and is credited with publishing the first fanzine, The Comet, in 1930. When Ziff-Davis moved its magazine production from New York to Chicago in 1938, it decided to replace the editor T. O'Conor Sloane. Since Palmer lived in nearby Milwaukee, he was offered the job.
His tenure at Amazing Stories is notable for his purchase of Isaac Asimov's first professional story, "Marooned Off Vesta," and for the controversial Shaver Mystery, which was based around a series of stories by Richard S. Shaver. In 1939, Palmer began a companion magazine to Amazing Stories entitled Fantastic Adventures, which lasted until 1953.
Palmer also began his own ventures while working for Ziff-Davis, eventually leaving the company to form his own publishing house, which was reponsible for his titles Imagination and Other Worlds, among others, although none of them lived up to the success of Amazing Stories during the Palmer years.
Palmer's support of Shaver's stories (which maintained that the world is dominated by insane inhabitants of the hollow earth) caused him to be shunned by many in the science fiction community. It is unclear how much Palmer believed of his own propaganda, or to what extent he was just pandering to the desires of his readership.
Palmer published Kenneth Arnold's reports of "flying discs," as well: he was instrumental in creating the popular beliefs in flying saucers. Palmer started Fate magazine, which ran many articles touting unpopular or paranormal beliefs, and one of his science fiction titles evolved into the magazine Flying Saucers.
An illustrated article about Palmers' publications (by Doug Skinner, written in 2002), with an emphasis on the colorful, limited-circulation magazines of his later years, is online at http://www.softcom.net/users/vtown/forum.html