Under the pseudonym Louis Masterson, he wrote a series of books about the fictitious Texas Ranger (later U.S. Marshal) Morgan Kane during 1966-1978. The 83 Morgan Kane books have been sold in more than 11 million copies. He has also written another nine book series known as the Diablo- and Diablito books.
Earlier in his career Hallbing used the pseudonyms Ward Cameron, Leo Manning, Lee Morgan and Colin Hawkins. His debut "Ubåt-kontakt" came in 1961, written under his real name. The same year came his first book set in the old West, "Portrett av en revolvermann" ("Portrait of a gunslinger"). In addition Kjell Hallbing was an eager weapons collector, resulting in his collection being one of the biggest private owned weapons collections in Norway at the time of his death. He also owned a little house at Bolkesjø, where he actually wrote most of the books in the Morgan Kane Series.
Before he started to write full-time in 1969, Hallbing worked as a bank-employee.