Born in 1966, Castellini made his comic book debut in 1989 with a story for Dylan Dog, a popular Italian horror character published by Sergio Bonelli Editore—and republished in America by Dark Horse—which was followed by another one in the September of the following year.
In 1991 he was the graphical creator of Nathan Never, also eventually republished by Dark Horse, a science-fiction series for which he drew covers until number 59.
Catellini states that his love for technical details, influenced by artists like Neal Adams and John Buscema, was perhaps at its best in his first story for Marvel Comics, a 1996 Silver Surfer graphic novel entitled Dangerous Artifacts written by his Predator: Demon's Gold collaborator Ron Marz.
This was followed by covers for Comic Powers Unlimited and Elektra Magazine, a stint on Fantastic Four Unlimited (1993-1995), and work on the miniseries crossover event Marvel vs. DC in 1996, all of which gained him a degree of popularity in the American comics market. Elsewhere for Dark Horse, Castellini also provided artwork for stories in the Star Wars Tales anthology.
In the past decade, Castellini has continued to work fairly extensively for both Marvel and DC/Wildstorm comics as an interior and cover artist. The artist's works have included Spider-Man, Conan the Barbarian, Red Sonja, and Batman: Gotham Knights, Captain Marvel, Blade, Thor, Wolverine: The End, and, most recently, Joker's Asylum II: Harley Quinn.
In 2006, Castellini joined the website comicpros.com