His earliest memory of reading comics is of a Spider-Man book featuring the Gibbon, illustrated by John Romita Sr., whom he cites as his primary artistic influence.

In 1993 he wrote and illustrated his own creator-owned horror character, Eudaemon, in the anthology Dark Horse Presents #72-74, for which he provided the first issue's cover.

He would later publish through Dark Horse a three-issue Eudaemon series, which he wrote, pencilled, and inked, and for which he provided airbrush-painted covers.

[1] His first work for DC Comics was interior art for Team Superman Secret Files and Origins #1, which was published in 1998.

In 1999, DeCastro worked for Marvel Comics, beginning with a painted cover and the interior art for X-Men: The Magneto War #1.

Although he mostly worked for Marvel Comics in the late 2000s, in 2008 DeCastro provided the interior pencils and inks for DC's Green Lantern Corps #21-22.