Jay Leonhart (born December 6, 1940) is an American double bassist, singer, and songwriter who has worked in jazz and popular music.

When Leonhart was fourteen he started playing double bass in the Pier Five Dixieland Jazz Band in Baltimore.

Leonhart has worked with Louie Bellson, Urbie Green, Jim Hall, Lee Konitz, Marian McPartland, Gerry Mulligan, Mike Renzi, Don Sebesky, Chuck Wayne, and Phil Woods.,[1] Thad Jones, Mel Lewis, Lou Marini, and Tony Bennett.

Leonhart has recorded many solo albums and has performed a one-man show called "The Bass Lesson" about his life in the music business.

With The New York Trio With Joe Beck With Louie Bellson With Barbara Carroll With Meredith D'Ambrosio With Michael Feinstein With Eddie Higgins With Peggy Lee With Maureen McGovern With Gerry Mulligan With Harold Ousley With others