Chiarello has been on staff at DC since 1993, joining the company after freelancing as an artist in comics and animation. Chiarello was hired as Color Editor - a then-new position in the comic industry, riding on the digital transition of that aspect of comics production. Chiarello was later elevated to Editorial Art Director, where he oversaw the art for the comics line and edited several limited series including Batman: Black & White, the Batman "Hush" arc, the Before Watchmen titles, New Frontier, Solo, and Wednesday Comics. He wrote the instructional book The DC Comics Guide to Coloring and Lettering Comics with Todd Klein.
While working at DC, Chiarello continued his illustration career, including work on Abrams Publishing's Heroes of the Negro League (with co-author Jack Morelli) and a 2009 Carhartt advertising campaign.
According to sources, Chiarello was amongst a small number of positions eliminated by DC - estimated at less than 3% of their workforce. In addition to Chiarello, SVP Sales Trade Marketing John Cunningham and VP Consumer Marketing Eddie Scannell were also among those whose positions were eliminated.