Oh came to prominence in Canada for her lead performance in the Canadian film Double Happiness (1996), playing Jade Li, a twenty-something Chinese Canadian woman negotiating her wishes and those of her parents.The film received critical acclaim, with Roger Ebert praising Oh's "warm performance." Oh won the Genie Award for Best Actress for the role. Her other Canadian films include Long Life, Happiness & Prosperity and Last Night, for which she again won a Best Actress Genie.Other films she has appeared in include The Night Listener, Sorry, Haters, Blindness, Bean, Wilby Wonderful, Hard Candy, and Rabbit Hole.She starred in the acclaimed Asian Canadian films Double Happiness, The Diary of Evelyn Lau, and Long Life, Happiness & Prosperity the formers of which won her the Genie Award for Best Performance by an Actress in a Leading Role and the Gemini Award for Best Performance by an Actress in a Leading Role in a Dramatic Program or Mini-Series respectively.
While at Sir Robert Borden High School she was Student Council President.
Cristina Yang on ABC's medical drama Grey's Anatomy, a role that earned her a Golden Globe, two Screen Actors Guild awards, as well as five nominations for Primetime Emmy Award for Outstanding Supporting Actress in a Drama Series.
She has also played notable roles in the feature films The Princess Diaries, Under the Tuscan Sun, Last Night, Sideways, and had a supporting role on the HBO original series Arliss.
She received an NAACP Image Award for Best Supporting Actress in a Comedy Series and a Cable Ace award for Best Actress in a Comedy for her work on Arliss.
In theatre, Oh has also starred in the world premieres of Jessica Hagedorn's Dogeaters at the La Jolla Playhouse and Diana Son's Stop Kiss at Joseph Papp's Public Theater in New York City.In 2002, Oh appeared in the family comedy Big Fat Liar, followed by a minor role in Steven Soderbergh's Full Frontal (2002).