 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., Thad Jones, Mel Lewis, Lou Marini, and Tony Bennett.He has worked as a studio musician in several genres, for musicians such as James Taylor, Ozzy Osbourne, and Queen Latifah.He has also played in a duo with trombonist Wycliffe Gordon.