Yost began his career in 2002 as an intern in Marvel Comics' west coast office. His spec film scripts got attention from Marvel executives who hired Yost to write episodes of the TV series Evolution. In 2003, Yost and Kyle co-wrote the episodes that introduced mutant character X-23, female clone of the popular X-Men character Wolverine. Marvel executives were impressed with X-23’s reception on TV, and asked Yost and Kyle to adapt the character into comics, first by writing a six-issue mini-series titled X-23: Innocence Lost, and then by taking over writing chores (as of issue #20) on the New X-Men title, bringing X-23 in as a regular character. Yost and Kyle also co-wrote a second X-23 six-issue miniseries, titled X-23: Target X.

Currently, Yost co-writes the latest incarnation of X-Force with Craig Kyle since the New X-Men title was canceled as of issue #46. Yost also recently wrote a five-issue mini-series titled Emperor Vulcan, a spin-off mini from the Uncanny X-Men story arc "The Rise and Fall of the Shi'ar Empire", featuring the third Summers brother, Gabriel (alias Vulcan), in his quest to bring stability to the struggling Shi'ar Empire after his successful coup d'etat against previous empress Lilandra. He is following this up with the Kingbreaker mini-series, which sets the scene for the War of Kings storyline Yost is also the writer of Battle School, the first in a series of adaptations of Orson Scott Card's Ender's Game by Marvel.

Yost has also written for such animated shows as Teenage Mutant Ninja Turtles and The Batman and was the story editor, head writer and show runner on the Fantastic Four animated series that aired on Cartoon Network in 2006. He also wrote the Young Avengers / Runaways crossover Secret Invasion story. He is currently the show runner for the Armored Adventures animated series, that started airing in 2008.

Yost was featured as the “Male Rising Star” in the Spring 2006 issue of Now Playing magazine.

Yost is also the writer for DC Comics' Red Robin that started in June 2009. He will be replaced by former Robin writer Fabian Nicieza.

Comics

• Marvel Comics
• X-23
• Innocence Lost #1-6 (with co-writer Craig Kyle and art by Billy Tan, 2005)
• Captain Universe/X-23 #1 (with co-writer Craig Kyle and art by Francis Portela, 2005)
• Target X (with co-writer Craig Kyle and art by Mike Choi, 2007)
• X-Force
• X-Force #1-28 (with co-writer Craig Kyle, Marvel Comics, 2008—2010)
• X-Force/Cable: Messiah War #1 (with co-writer Craig Kyle and art by Mike Choi, 2009)
• X-Force: Sex and Violence #1-3 (with co-writer Craig Kyle and art by Gabriele Del'Otto, 2010)
• X-Men
• X-Men Unlimited Vol. 2 #11 (first story only, with pencils by Billy Dallas Patton, 2005)
• New X-Men #20-46 (with co-writer Craig Kyle, 2006—2008)
• Emperor Vulcan #1-5 (with pencils by Paco Diaz and Vincente Cifuentes, 2008)
• X-Men Origins: Colossus #1 (with penciles by Trevor Hairsine, 2008)
• X-Men: Divided We Stand #1 (Gentle and Hellion stories only, 2008)
• X-Men: Worlds Apart #1-4 (art by Diogene Neves, Marvel Comics, 2008—2009)
• X-Men: Kingbreaker #1-4 (with Dustin Weaver, Marvel Comics, 2008—2009)
• Dark X-Men: The Confession #1 (with co-writer Craig Kyle and art by Yanick Paquette, 2009)
• X-Men: Second Coming #1-2 (#1 with co-writer Craig Kyle and art by David Finch; #2 with co-writers Matt Fraction, Mike Carey and Zeb Wells and art by Adi Granov, 2010)
• X-Men: Second Coming — Revelations: Hellbound #1-3 (with Harvey Tolibao, 2010)
• X-Men: To Serve and Protect #1-? (2010)
• Other Marvel
• Spider-Man Unlimited Vol. 3 #9 (first story only, with pencils by Drew Johnson, 2005)
• Wolverine: Killing Made Simple (first story only, with pencils by Koi Turnbull, 2008)
• Runaways/Young Avengers #1-3 (art by Takeshi Miyazawa, 2008)
• Runaways Vol. 3 #10 (with co-writer James Asmus and art by Sara Pichelli & Emma Rios, Marvel Comics, 2009)
• Marvel Assistant-Sized Spectacular #2 (writer of the Elsa Bloodstone story, Marvel Comics, 2009)
• Enders Game: Command School #1-5 (art by Pasqual Ferry, 2009—2010)
• Breaking Into Comics the Marvel Way! #1 (X-Men story only with art by Paul Davidson, 2010)
• Psylocke #1-4 (art by Harvey Tolibao, 2009—2010)
• Nation X #1, 3 (#1 Iceman story only; #3 Box & Diamond Lil story only, 2010)
• The Many Loves of The Amazing Spider-Man #1 (Black Cat story only with art by Michael Ryan, 2010)

• DC Comics
• Batman: Battle for the Cowl - The Underground #1 (with art by Pablo Raimondi, 2009)
• Red Robin #1 - 12 (with art by Ramon Bachs, 2009—2010)
• Titans #16 (with art by Angel Unzueta, 2009)
• Batman: Streets of Gotham #5-6 (main feature, with art by Dustin Nguyen, 2009)

• Image Comics
• Killer of Demons #1-3 (Art by Scott Wegener 2009)

Film & television

• Evolution TV Series (writer)
• 3.11 - X23 (story by Craig Kyle, co-written with Craig Kyle), 2003
• 3.12 - Dark Horizon Part 1 (co-written with Craig Kyle), 2003
• 3.13 - Dark Horizon Part 2 (co-written with Craig Kyle), 2003
• 4.03 - Target X (co-written with Craig Kyle), 2003
• The Batman TV Series (writer)
• 1.07 - The Big Heat (co-written with J.D Murray), 2004.
• 2.02 - Riddled (co-written with J.D Murray), 2005
• 2.06 - The Pets (co-written with J.D Murray), 2005
• 3.04 - RPM, 2005
• Teenage Mutant Ninja Turtles (writer)
• 3.25 - Exodus Part 1, 2005
• 4.01 - Cousin Sid, 2005
• 4.13 - Samurai Tourist, 2005
• 5.01 - Lap of the Gods, 2008
• 5.13 - Enter the Dragons Part 2, 2008
• Legend of the Dragon (writer)
• 1.16 - Shell Game, 2006
• Alien Racers (writer)
• 1.18 - Skrash and Burn, 2006
• World's Greatest Heroes (head writer, story editor, show runner)
• 1.03 - Doomsday (story by Craig Kyle), 2006
• 1.12 - Annihilation (story by Craig Kyle), 2007
• 1.18 - The Cure (story by Craig Kyle & Dan Slott), 2007
• Heroes of Tomorrow (writer), 2008
• Wolverine and the X-Men (writer)
• 1.07 - Wolverine vs. Hulk, 2008 (story by Greg Johnson, Craig Kyle & Christopher Yost)
• 1.09 - Future X, 2008 (story by Greg Johnson & Craig Kyle)
• 1.10 - Greetings From Genosha, 2008 (story by Greg Johnson & Craig Kyle)
• 1.12 - Excessive Force, 2008 (story by Greg Johnson, Craig Kyle & Christopher Yost)
• 1.13 - Battle Lines, 2009 (story by Greg Johnson, Craig Kyle & Christopher Yost)
• 1.14 - Stolen Lives, 2009 (story only, with Greg Johnson & Craig Kyle)
• 1.15 - Hunting Grounds, 2009 (story only, with Greg Johnson & Craig Kyle)
• 1.16 - Badlands, 2009 (story only, with Greg Johnson & Craig Kyle)
• 1.18 - Backlash, 2009 (story by Greg Johnson, Craig Kyle & Christopher Yost)
• 1.19 - Guardian Angel, 2009 (story only, with Greg Johnson & Craig Kyle)
• Hulk Vs (co-written with Craig Kyle), 2009
• Armored Adventures (head writer, story editor, show runner)
• 1.01 - Iron Forged in Fire Part 1, 2009
• 1.02 - Iron Forged in Fire Part 2, 2009
• 1.12 - Seeing Red, 2009
• 1.19 - Technovore, 2009 (story only)
• 1.25 - Tales of Suspense Part 1, 2009
• 1.26 - Tales of Suspense Part 2, 2009