Coles Trapnell was born in New York and was educated at Virginia Military Institute and New York University. His early career was as a journalist before entering the film industry in 1936 as a script reader for the RKO studio.
He later moved to 20th Century Fox as a Story Editor and Associate Producer and the in 1954 to Television, firstly as a story editor for Four Star Playhouse
and later as a writer and producer for Maverick
. He also wrote scripts for two other western series - Lawman
and Yancy Derringer