While studying creative writing at Sarah Lawrence College, Tynion met and began studying under Scott Snyder. Following school, he became an intern for the Vertigo imprint of DC Comics.
After a few years working in advertising, Scott Snyder asked Tynion to co-write the back-up features for the New 52 relaunch of Batman, starting with Batman #8 with artist Rafael Albuquerque. Tynion went on to co-write Batman Annual #1 with Snyder, for artist Jason Fabok. He also launched a spin-off of the Night of the Owls storyline with the ongoing comic series Talon, which ran for 18 issues and followed up Talon with a brief stint on the title Red Hood and the Outlaws.
In 2013, he paired with artist Jeremy Rock to co-create his first original comic series, The Eighth Seal, for Mark Waid’s digital comic publisher Thrillbent. Tynion followed up the series with an additional horror comic for Thrillbent, The House In The Wall, co-written by Noah J. Yuenkel and drawn by Eryk Donovan.
In 2014, Tynion was named as one of the head writers of Batman Eternal. He also launched the original series The Woods, for BOOM! Studios, with Greek artist Michael Dialynas. He followed up The Woods with a three-issue apocalyptic horror miniseries titled Memetic, which paired him with artist Eryk Donovan once again.
In 2015, Tynion was announced as one of the co-writers of the new Constantine: The Hellblazer series alongside Ming Doyle and artist Riley Rossmo. He also took on the role of show runner for the weekly series Batman & Robin Eternal.Tynion also was announced as the writer of the Batman/Teenage Mutant Ninja Turtles crossover with DC and IDW Publishing. The series launched in December 2015. He also launched two new creator owned series through Boom! Studios, UFOlogy, co-written by Noah J. Yuenkel with art by Matt Fox, and Cognetic, the sequel to Memetic with artist Eryk Donovan.
In 2016 he became the writer of the biweekly Detective Comics for DC’s Rebirth initiative.
Tynion has worked on a number of additional titles for DC Comics, BOOM! Studios, Marvel Comics, IDW Publishing, and Thrillbent.