As an editor, he oversaw numerous comic books featuring the Justice League, including series starring various members of that team such as Batman, Aquaman, Martian Manhunter, Green Lantern, and the Flash.

Batman was the first superhero who entered his consciousness, as it was the first character he dressed up as for Halloween, and the first comic book whose creators he recognized.

[5] Tomasi wrote the Nightwing title for 14 issues until its cancellation in April 2009 due to events in the "Battle for the Cowl" storyline.

[9] From 2009 to 2010, Tomasi co-wrote the creator-owned title The Mighty with Keith Champagne,[10][11] as well as Green Lantern Corps through the "Blackest Night" storyline.

[13][14] During that same period, he was the regular writer on the monthly Green Lantern: Emerald Warriors and The Outsiders, which ended in 2011 as part of DC's The New 52 line-wide relaunch.

[28][29] The series' premise is based on the idea that Manapul explains thus: "The best place to hide when you're in the Witness Protection Program perhaps is through a different time.

"[30] The story depicts a 26th century dysfunctional family who when threatened, flee by traveling through time to the year 2024, where they to encounter the strange inhabitants and culture of that era, only to find that the threat they thought they had escaped has followed them.

In a February 2011 interview with Comic Book Resources, Tomasi discussed how his then-eight-year-old son influenced his approach to writing Damian Wayne in Batman and Robin.