His work is characterized by his use of dynamic figure work (particularly evident in his Spider-Man work), and panel composition that often involves shifting of the camera eye and perspective.
His well-known works include various sporadic fill-in issues of The Uncanny X-Men and The New Mutants, as well as runs on Cloak and Dagger, Spider-Man 2099, Nightwing, Batgirl, and Green Lantern Versus Aliens.
He is credited, along with fellow illustrator Mike Zeck, of designing the black-and-white costume to which Spider-Man switched during the 1984 Secret Wars miniseries, and later wore for a time. According to the Spider-Man 1/2 special, the costume began as a design by Zeck that Leonardi embellished. The plot that developed as a result of Spider-Man's acquisition of the costume led to the creation of the Spider-Man villain known as Venom.
His most recent works have included the 2005 four-issue miniseries, Star Wars: General Grievous the 2006 movie tie-in, Superman Returns Prequel #3, Superman #665 and #668 (2007), JLA: Classified #43 (November 2007), and Witchblade #112 (January 2008).
Comics work includes: