Immerman often hung around his father's nightclub in Harlem, and he came to know many musicians and songwriters there. It was through these connections that he got his first job, as a designer of sheet music covers. He was extremely succesful: at one point his signature could be found on some 80 % of all sheet music published in New York. 
He later switches from sheet music work to book cover work; his first paperback cover was for Pocket Books 123, Dr. Jekyll and Mr. Hyde. He established his own design studio, located at 48 West 48th Street, in 1942; his partner was H. Lawrence Hoffman, their first employee was Robert Holly, and the signature IM-HO, which can be found on several Pocket Book and Popular Library covers, stands sometimes for Immerman and Hoffman and sometimes for Immerman and Holly. 
The studio produced covers for both hardcover and paperback publishers, and had some 40 firms as clients. 
After several years of serving as parttime art director at Pocket Books in addition to his duties at the studio, Immerman became full-time art director for that house in 1947 and turned the studio over to Hoffman. 
He stayed at Pocket Books through 1975. 
A collegue says that, although Immerman was a good artist and calligrapher, he was often to busy to produce good work. There were times when he had to design five covers himself and supervise the design of a dozen others, all in the space of a few days. Some of his own covers were quite good; others, to be kind, were not. 
In the late 1970s he was employed as art director for Penguin Books. He was, in 1981, a consultant, working out of his home in Yonkers, New York.