Born in Nepean, Ontario, Canada, Oh was raised by her father, Joon-Soo, a businessman, and her mother, Young-Nam, a biochemist. Both her parents emigrated from Korea to Canada in the late-1960s. As a child, she entered ballet class at the age of 4 and landed her first role at 10, playing The Wizard of Woe in a school production of "The Canada Goose." Oh was a busy student at Sir Robert Borden High School in Ottawa, where she was a member of the drama club; founder of the environmental club, Borden Active Students for the Environment (BASE), Student Council President; and a member of both the volleyball and cross-country skiing teams. After getting her professional start at 15 on television and in commercials, she turned down a four-year journalism scholarship to Carleton University in order to pay her own way at the National Theatre School of Canada as a drama student. Meanwhile, Oh made her onscreen debut in Marc Voizard's short film "The Journey Home" (1989). After graduating college, Oh immediately had a breakout role starring in "The Diary of Evelyn Lau" (CBS, 1993), a fact-based tale of a young woman who falls into a life of drugs and prostitution. Her impressive performance won Oh a great deal of acclaim and recognition, including a nomination for a Gemini Award. She followed up that same year with a starring role in the CBC biopic "Adrienne Clarkson Presents," in which she played the titular Canadian broadcaster. In 1995, Oh advanced her career with an award-winning portrayal of a young Chinese-Canadian woman struggling to live her own life and break free from her family's oppressive traditions in "Double Happiness." Oh proved a remarkable onscreen presence, brimming with an understated, but nevertheless luminous vitality and charm. She capably handled both the lighter romantic moments and the more tension-filled family clashes. For her multi-layered work, she was awarded that year's Best Actress Genie - the Canadian equivalent of an Academy Award.After a failed attempt at breaking through on U.S. television with a recurring role on the quickly cancelled sitcom "If Not For You" (CBS, 1995), Oh won the part of Rita, an overworked and underpaid assistant to tactless sports agent Arliss Michaels (Robert Wuhl), on the HBO comedy "Arli$$" (1996-2002). She was awarded a 1997 CableACE Award for her performance and proved her comic bona fides while exposing her talents to an American audience. The short, 13-episode seasons on "Arli$$" gave Oh an opportunity to remain active in features, including memorable turns in "Bean" (1997) and "Permanent Midnight" (1998). She then took the lead role in Don McKellar's acclaimed Armageddon-themed "Last Night" (1998). Thoughtful and straightforward, "Last Night" followed several residents of Toronto and their last few hours on Earth before a mysterious, but preordained apocalyptic event. Oh played a woman whose car is vandalized in the rioting surrounding the final day and is unable to get home or to reach her husband (David Cronenberg), with whom she had planned to commit suicide. But then things change after meeting Patrick Wheeler (McKellar), a man more than happy to spend his last hours alone. Oh's performance in the quietly fascinating feature was both impressive and unsettling, and earned the actress her second Genie Award.Sticking with Canadian films, Oh was featured in "The Five Senses" and Francois Girard's "The Red Violin" (1998), an epic tale that followed the travels of the titular instrument throughout the centuries. She was next featured in Audrey Wells' "Guinevere" (1999), playing a protégée of Connie (Stephen Rea), an artist and procurer of young women. Also that year, Oh had a two-episode stint as a no-nonsense faculty member on high school teen drama "Popular" (WB, 1999-2001). On the big screen, she had one of her best roles playing a romantically challenged exotic dancer fond of writing poetry in Michael Radford's "Dancing at the Blue Iguana" (2000), which revolved around the lives of several strippers at a Los Angeles club and starred Daryl Hannah and Jennifer Tilly. Meanwhile, she played a school principal in Garry Marshall's teen Cinderella fantasy "The Princess Diaries" (2001), before landing a significant role as Bambi Kanetaka in the ensemble cast of Armistead Maupin's "Further Tales of the City" (Showtime, 2001) and a recurring part as police detective Shelly Tran on "Judging Amy" (CBS, 1999-2005). Oh then landed a supporting turn in the Frankie Muniz kid revenge comedy "Big Fat Liar" (2002) and had a cameo as a fired employee in Steven Soderbergh's failed A-list indie effort, "Full Frontal" (2002). Oh continued to up her profile by playing Patti, one of Diane Lane's sympathetic gal pals who sends her on a trip to Tuscany to shake off her romantic malaise, in the romantic comedy "Under the Tuscan Sun" (2003). But it was her next film which made her a household name. In the buddy picture "Sideways" (2004), Oh played a somewhat liberal-minded winery employee who becomes romantically entangled with a libidinous bridegroom (Thomas Hayden Church) on a pre-wedding road trip engineered by his down-and-out best friend (Paul Giamatti). Written and directed by Oh's husband Alexander Payne, "Sideways" earned massive critical acclaim for all involved, though the film became a bittersweet moment in time for the couple, as Payne and Oh announced their split shortly after the 2005 awards season. Professionally speaking, however, things were looking up for the actress when she shifted to the small screen by landing the role of the emotionally-bottled and manipulative physician Cristina Yang in the ensemble medical drama "Grey's Anatomy" (ABC, 2005-). To the surprise of nearly everyone involved, the show was an overnight smash, with diehard fans following the cast's every move both on screen and off. Over the course of several seasons, Cristina had a complicated interracial romance with a cocky surgeon (Isaiah Washington), only to find herself abandoned by him at the altar. Oh won a Golden Globe and a Screen Actors Guild award while earning consecutive Emmy nominations for Outstanding Supporting Actress in a Drama Series from 2005-09. Maintaining a regular presence in feature films during her "Grey's" tenure, Oh starred in "The Night Caller" (2006), an adaptation of Armistead Maupin's bestselling thriller about a late night radio host who strikes up a friendship with a young listener with a suspicious hard-luck story. Oh enjoyed brief screen time in the Christopher Guest-penned Hollywood satire "For Your Consideration" (2006), which she followed with a meatier supporting role as the Ministry of Health in the unsuccessful epidemic thriller, "Blindness" (2008). In August 2013, Oh announced that she would be leaving "Grey's Anatomy" after the show's upcoming tenth season.