His father worked for General Motors (GM), as a site locator for GM facilities, which caused the family to move frequently. Although Leonard was born in New Orleans, he did not live there for long. The family moved often until he was nine, in 1934, when they settled in Detroit, Michigan.

About this time, two major influences occurred that would show up in many of his works. Gangsters such as Bonnie and Clyde were making national headlines, as were the Detroit Tigers baseball team. In the early 1930s, Bonnie and Clyde were on their rampage, and were killed in May, 1934. The Tigers made it to the World Series in 1934. Leonard turned these events into lifelong fascinations with both sports and guns.

Leonard graduated from the University of Detroit Jesuit High School in 1943.

Leonard, or "Dutch" as he is sometimes called, got his first breaks in the fiction market during the 1950s, regularly publishing pulp western novels. He has since forayed into mystery, crime, and more topical genres, as well as screenwriting. He has been commended by critics for his gritty realism and strong dialogue. His writing style sometimes takes liberties with grammar in the interest of speeding along the story. In his essay "Elmore Leonard's Ten Rules of Writing, Leonard wrote, "My most important rule is one that sums up the 10: If it sounds like writing, I rewrite it."

Leonard has been called "the Dickens of Detroit" because of his intimate portraits of people from that city. Leonard's ear for dialogue and ability to render dialogue on the printed page are uncanny and have been praised by writers as diverse as Saul Bellow and Martin Amis. "Your prose makes Raymond Chandler look clumsy", Amis told Leonard at a Writers Guild Theatre event in Beverly Hills in 1998.

A number of Leonard's novels have been adapted as films, perhaps most notably Get Shorty in 1995, and Rum Punch as the 1997 film Jackie Brown.

Leonard now lives in Oakland County, Michigan. Many of his more recent novels are set in Metro Detroit.