Though his first published work was a short story in Cosmos magazine in 1953, his career as a writer can be said to have started in 1959 when he began writing for Astounding and Galaxy Science Fiction.
He co-wrote the first novel in the "Psi-Power" series: Brain Twister, written with Randall Garrett under the joint pseudonym Mark Phillips.
Janifer's best known work is the "Survivor" series, comprising five novels and many short stories.
The series follows the career of Gerald Knave as he visits (and survives to tell the tale of) planets on the outskirts of the civilized galaxy.
In addition to his career as a novelist and short story author, Janifer was an editor for Scott Meredith Literary Agency; editor/managing editor of various detective and science fiction publications; film reviewer for several magazines; and a talented pianist.