Between college and graduate school, he worked on staff in the editorial department of DC Comics, while also co-writing Captain Atom with Cary Bates.

In 1985, Weisman wrote a four-issue mini-series for DC Comics starring the superheroine Black Canary, which was cancelled due to the character being used in writer/artist Mike Grell's series Green Arrow: The Longbow Hunters.

[8] At San Diego Comic-Con 2022, It was announced that Dynamite Entertainment had acquired the Gargoyles license and that Weisman would serve as the writer of these new comics.

[9] In November 2023, it was announced that Weisman would write a new ongoing series for Marvel Comics dubbed The Spectacular Spider-Men, which features Peter Parker and Miles Morales teaming up and fighting supervillains together.

[10] After leaving Disney in 1996, Weisman spent two years at DreamWorks, where he created and developed a new television series called Rain of the Ghosts.

Weisman has announced that the third book will be titled Masque of Bones, and in 2015, he released a full-cast unabridged AudioPlay based on Rain of the Ghosts after successfully crowdfunding the project through Kickstarter.

Alexander Sowa, for CBR, highlighted that "Greg Weissman's War of the Spark: Ravnica [was] infamous among fans for its misrepresentation of existing characters".

[14] Sowa commented that its sequel, War of the Spark: Forsaken, "was greeted with a lukewarm response after it infamously attempted to retcon the sexuality of one of the book's protagonists, Chandra.

[15] Reactions to the sequel[16][17] were "overwhelmingly negative"[18] and it was "lambasted for its disappointing prose, lack of understanding of character voice, and failure to provide any emotional payoff for the relationships that have been set up in the world of Magic.