After serving in the Navy during World War II, he majored in English at the University of Detroit. He started writing copy for an advertising agency before his graduation in 1950.
He married three times: to the late Beverly Cline in 1949, the late Joan Shepard in 1979, and at the age of 68, to Christine Kent in 1993. He had five children, all from his first marriage.
His son, Peter, followed in his father's path, going into advertising for years before achieving his own success as a novelist with his 2008 debut, "Quiver."
In 2012, after learning he was to become a National Book Award lifetime achievement recipient, Leonard said he had no intention of ending his life's work.
"I probably won't quit until I just quit everything — quit my life — because it's all I know how to do," he told the AP at the time. "And it's fun. I do have fun writing, and a long time ago, I told myself, 'You got to have fun at this, or it'll drive you nuts.'"
Associated Press writer Hillel Italie contributed to this report.