Leishman rolled in a 50-footer and then made clutch up-and-down pars at the final two holes at Bay Hill to secure his second PGA Tour victory and an invitation to the April 6-9 Masters.
He carded 69 to finish at 11-under-par 277.
Americans Charley Hoffman (73) and Kevin Kisner (73) tied for second on 10-under after sharing the overnight lead.
Northern Irishman Rory McIlroy (69) three-putted the last to finish two strokes behind.
Read the original article on Eurosport: Leishman wins Arnold Palmer Invitational by one stroke