His first fiction sale was the short story “And Not Quite Human,” published in the September 1953 issue of Beyond Fantasy Fiction. His first published novel was The Color of Hate in 1960. He had 20 more novels and collections published (over half of them in the series featuring Indiana circuit judge Donald Robak, which began with 1971’s Deliver Us to Evil) and around 100 short stories. His collaborators in science fiction included Alexei Panshin and Harlan Ellison; he co-wrote one mystery novel (Loose Coins) with fellow Indiana prosecuting attorney Guy M. Townsend. His last novel, Snowbird’s Blood, was published in February 2008. Many of his mystery novels were set in the fictitious Bington, a place which combined aspects of Madison and Bloomington.

Hensley remained active in science fiction fandom throughout his life; the Hensleys were familiar faces at science fiction conventions such as Rivercon and Midwestcon. Hensley was a First Fandom “Dinosaur” (which meant he had been active in fandom prior to July 4, 1939), and received the First Fandom Hall of Fame Award in 2006.