Valentino began his career in the late 1970s creating small press and mostly autobiographical comics. The early-mid 1980s saw normalman which first appeared as a back-up story in Aardvark-Vanaheim's Cerebus. Aardvark-Vanaheim's Dave and Deni (Dave's wife at the time) began publishing normalman as a 13 issue limited series but only did so until #8, when Deni began her own publishing company, Renegade Press which finished the series. Renegade also published three issues of his self-titled series, Valentino in the mid-late 80s.
In the late 80s he began working for Marvel Comics on their super-hero titles. His most notable work for the company was as writer and artist on the future-set super-hero series Guardians of the Galaxy and selected issues of What If...? plus fill-ins on most of Marvel's major titles.
He left Marvel in 1992 to co-found Image Comics with Erik Larsen, Jim Lee, Rob Liefeld, Todd McFarlane and Marc Silvestri. Valentino originated several projects at Image, which he published through his own Shadowline imprint. Unlike at Marvel, where Valentino worked on characters owned by that company, the original Shadowline titles were all creator-owned.
Of these the titles the most notable was the super-hero series ShadowHawk, on which he was both writer and artist. In 1997 he began another series in black and white called A Touch of Silver, a semi-autobiographical novel about a young comic book fan coming of age in the 1960s. Also during this time he repackaged most of his earliest autobiograpical work into a trade paperback called Vignettes, with an introduction by Dave Sim.
In 1999 he became the publisher of Image Comics. Under his directorship the company diversified its line considerably. The results were mixed. On one hand, Valentino's efforts led to the discovery of a number of talented creators, including Robert Kirkman and Brian Michael Bendis. On the other hand Image Comics saw a drop in overall sales. Still, he was able to turn the company's first profit in nearly a decade by opening new revenue streams such as sales to traditional book stores and libraries. The company managed to maintain its standing as number three in overall market share.
In 2003, Valentino was replaced as publisher of Image Comics by Erik Larsen, another co-founder of the company. Since then Valentino has resurrected Shadowline, his own arm of Image and has published a wide variety of books including a revived ShadowHawk series, The Collected normalman, a new auto-bio book, Drawing From Life as well as creator owned properties including Bomb Queen, After the Cape and Sam Noir. He also serves on the board of directors of the comic industry charity The Hero Initiative. In 2008 Valentino created Silverline Books an all-ages imprint for original graphic novels.
