- "Marvel contacted me not long after the agreement with Lucasfilm was finalized. They knew I was quite a fan and guessed I'd be interested. They weren't wrong! Star Wars means a lot to me."
- ―John Cassaday
In 1996, Cassaday went to San Diego Comic-Con International and showed his portfolio to Mark Waid, who was impressed with the young artist's work. He soon began getting several job offers, and subsequently worked on Dark Horse Comics' comic series, Ghost.
His primary output are covers, but he has also penciled several comic series, such as Warren Ellis's Planetary, Joss Whedon's Astonishing X-Men (for both of which he received Eisner Awards), the first four issues of Uncanny Avengers, as well as several issues of Captain America under the Marvel Knights imprint. He also provided artwork for the French comic book Je suis légion (I Am Legion).
- "Launch Pad"—Star Wars Insider 152
- "Blaster"—Star Wars Insider 155
- "Marvel Comics 2015: A Marvel Galaxy"—Star Wars Insider 158
- "Blaster"—Star Wars Insider 164