He began his writing career with the short film Talk to Taka in 2000. He made his television writing debut with an episode of The O.C. in 2003. He co-wrote the first season episode "The Homecoming" with the series creator Josh Schwartz.
He next wrote for the series October Road in 2008. He wrote the second season episodes "Revenge of the Cupcake Kid" and "The Fine Art of Surfacing". He also wrote for the new action series Samurai Girl in 2008. He wrote the episodes "Book of the Shadow: Part 1" and "Book of the Sword: Part 2".
In fall 2008 he joined the staff of the American remake of science fiction drama Life on Mars. He was an Executive Story Editor for the show's sole season. The series was developed by Josh Appelbaum, Andre Nemec, and Scott Rosenberg, who created October Road. Oh wrote the episode "The Real Adventures of the Unreal Sam Tyler", co-wrote the episode "Dark Side of the Mook" with Tracy McMillan, and co-wrote the episode "Coffee, Tea, or Annie" with Adele Lim.
In fall 2009 he was a co-producer and writer for the new drama series Happy Town. The show was created by Applebaum, Nemec, and Rosenberg. Oh wrote the episode "Dallas Alice Doesn't Live Here Anymore". The show was canceled during production and the episodes were eventually aired in summer 2010.
Following the cancelation of Happy Town he joined the crew of the supernatural drama The Vampire Diaries as a co-producer for the latter part of the first season. He joined the production team for the fifteenth episode "A Few Good Men". Oh co-wrote the episodes "There Goes the Neighborhood" with Andrew Chambliss, and "Miss Mystic Falls" with Caroline Dries, and co-wrote the season finale "Founder's Day" with Chambliss.
In 2011 he joined the crew of the new medical drama Body of Proof as a producer. The series began airing as a midseason replacement. He returned as a producer for the second season in fall 2011 and wrote the episode "Point of Origin".