Cohn was born in Freeport, Illinois, but subsequently moved to Cleveland, Ohio where he began work as a newspaper editor and journalist. He then moved to Galveston, Texas, where he ran a newspaper.
Following his career in journalism, he moved to Arizona and participated as a secretary in the Arizonaconstitutional convention which led to its statehood in 1912.
In the 1920s, he moved to Los Angeles, California and began working as a writer, first doing title cards for silent films and, later, scripts and adaptations. He was a co-writer on the 1926 film The Cohens and Kellys, the first of the six-film Cohens and Kellys franchise. His work on adapting The Jazz Singer, one of the first motion pictures with sound, from a play and short story by Samson Raphaelson, led to his first and only nomination for an Academy Award. During this period, he was a prolific writer and wrote more than 100 scripts, roughly 40 of which were produced into films.
In the 1930s, he retired from screenwriting and was appointed the Police Commissioner of Los Angeles, and he continued writing as a short story writer. He died of a heart condition in 1951.
