Greene spent several years working in Rhodesia as a civil servant, before being discharged with a back injury. By 1913, Greene had emigrated to the US, become a citizen and settled in Boston. In 1918, he began to write fiction based on his experiences for the pulp magazines.

Greene's earliest stories were published in the US Adventure magazine, where he created his most famous series of stories featuring the Major and his Khoikhoi friend Jim. For a time, Greene worked as Assistant Editor on Adventure and began writing for other pulp magazines, including Short Stories, Action Stories, Argosy, Blue Book and Everybody's Magazine.