During Casey's run at Marvel Comics people started to recognize his talent as a writer, especially in regard to his work on the book Cable. He took the story in a different direction than had been previously established. Cable went from a multi-gun toting tough guy to a more spiritualized leader for the Askani.

Casey wrote many titles for Wildstorm comics, often to high critical acclaim, like the highly experimental Automatic Kafka with artist Ashley Wood. Casey took over Wildcats and gave the series new direction turning from standard superheroics to corporate espionage. His Mister Majestic series with artist Ed McGuiness impressed DC Comics enough to offer them a run on Adventures of Superman.

Casey wrote a limited series for Marvel Comics, a sequel to 2005's Avenger's: Earth's Mightiest Heroes. He also wrote the series America's Elite for Devil's Due Publishing and Gødland for Image Comics. He is also wrote a revamp of the original Youngblood miniseries by Rob Liefeld, called Maximum Youngblood. Recently, as well, as discussing the ending of Gødland and the new Charlatan Ball and Nixon's Pals, he mentioned that Codeflesh would be returning.

Casey is a part of the Man of Action collective of creators (along with Joe Kelly, Duncan Rouleau, Steven T. Seagle), who created the series Ben 10, currently airing on Cartoon Network.

Dark Reign: Zodiac pits a new iteration of the old Avengers enemies against Norman Osborn's new status quo, and Final Crisis: Aftermath: Dance follows the adventures of the Super Young Team.

He currently writes Avengers: The Origin (2010).

DC Comics

DC Comics work includes:

• The Flash #151 (1999)
• The Adventures of Superman #587-590, 592-606, 608-610, 612-623 (2001—2004)
• Batman: Tenses #1-2 (2003)
• Final Crisis Aftermath: Dance #1-6 (with ChrisCross, 2009)

Marvel Comics

Marvel Comics work includes:

• Alpha Flight volume 2 #11 (1998)
• Alpha Flight/Inhumans Annual '98 (1998)
• Uncanny X-Men/Fantastic Four Annual '98 (1998)
• Wolverine: Black Rio (1998)
• Cable #51-70 (1998—1999)
• The Incredible Hulk #467-474 (1998—1999)
• Wolverine/Cable: Guts and Glory #1 (1999)
• Wolverine: Days of Future Past #2-3 (1998)
• X-Men #73 (1998) and 88 (1999)
• Iron Man Annual '99 (1999)
• Juggernaut: The Eight Day (1999)
• Thunderbolts #26 (1999)
• Captain America Annual '99 (1999)
• Uncanny X-Men #368, 394-409 (1999, 2001—2002)
• Deathlok (vol. 3) #1-11 (1999—2000)
• Children of the Atom #1-6 (1999—2000)
• Heroes Reborn: Masters of Evil (2000)
• Uncanny X-Men Annual 2001 (2001)
• The X-Men In: Life Lessons (2003)
• Avengers: Earth's Mightiest Heroes #1-8 (2005)
• Iron Man: The Inevitable #1-6 (2005—2006)
• Avengers: Earth's Mightiest Heroes II #1-8 (2006—2007)
• Fantastic Four: First Family #1-6 (2006)
• Enter the Mandarin #1-6 (2007—2008)
• The Last Defenders #1-6 (2008)
• Dark Reign: Zodiac #1-#3 (with Nathan Fox, 2009)
• Avengers: The Origin (2010)

Wildstorm

Wildstorm titles include:

• Gen¹³ #42 (1999)
• Mister Majestic #1-9(1999—2000)
• The Authority: Devil's Night (2000)
• Wildcats: Devil's Night (2000)
• Wildcats: Ladytron (2000)
• Wildcats volume 2 #5, #8-28 (2000—2002)
• Automatic Kafka #1-9 (2002)
• Wildcats v3.0 #1-24 (2002—2004)
• Coup D'Etat: Wildcats (2004)
• The Intimates #1-12 (2004—2005)

Image Comics

Titles published by Image Comics include:

• Hellcop #1-4 (with Gilbert Monsanto, 1998—1999)
• "Codeflesh" (with Charlie Adlard in Double Image #1-5, 2001)
• Gødland #1-ongoing (with Tom Scioli, 2005-ongoing)
• Image Comics Holiday Special 2005 (4-page Gødland story, 2005)
• Krash Bastards, (with Axel 13, graphic novel, 2008)
• Nixon's Pals (with Chris Burnham, graphic novel, 120 pages, April 2008, ISBN 1582409374)
• Charlatan Ball #1-6 (with Andy Suriano, June 2008 - February 2009, tpb, collects Charlatan Ball Season One #1-6, 160 pages, April 2009, ISBN 1607060841))

AiT/Planet Lar

For AiT/Planet Lar he has produced:

• Codeflesh (with Charlie Adlard, Image Comics, tpb, collects Double Image/Double Take #1-8, softcover, 144 pages, AiT/Planet Lar, November 2003, ISBN 1932051155, hardcover, Codeflesh: The Definitive Edition, 128 pages, Image Comics, March 2009, ISBN 1607060779)
• Full Moon Fever (with Caleb Gerard and Damian Couceiro, graphic novel, 88 pages, September 2005, ISBN 193205135X)
• Rock Bottom (with Charlie Adlard, graphic novel, 112 pages, 2006, ISBN 1932051457)

Others

Work for other publishers includes:

• Battle Pope #11-13 (Funk-O-Tron, 2000)
• Double Take #6-8 (Funk-O-Tron, 2001)
• Weird Tales #2 (Dark Horse Comics, 2003)
• Milkman Murders #1-4 (with Steve Parkhouse, Dark Horse Comics, 2004)
• Infantry #1-3 (Devil's Due Publishing, 2004—2005)
• Tom Strong #33 (America's Best Comics, 2005)
• America's Elite #0-18 (Devil's Due Publishing, 2005—2006)