Q was born and raised in Honolulu, Hawaii. Her father works for the government, and is American of Irish and Polish descent. Her mother works on a golf course, and is a Vietnamese immigrant who had come to the U.S. with no money, and could not speak English. Her parents met while her father was stationed in Vietnam during the war. Q grew up with four siblings.
Q attended Mililani Waena Elementary School and Wheeler Intermediate School. She also attended Mililani High School, where she was on the cross country, track and field, and swim teams. She won the title of "Best Bod" senior year, and graduated from Mililani High School in 1997.
At the suggestion of a friend, Q began modeling in Tokyo at the age of 17, before making an unsuccessful move to Taipei, and finally trying in Hong Kong. She has said it was not easy for her: "I had twenty bucks in my pocket. I mean, I literally did the same thing that my mother did when she left Vietnam... didn't speak the language... had no money." But, it was in Hong Kong, that she was selected by Jackie Chan, because he saw a potential action star. His intensive training taught her the importance of professionalism and always doing her own stunts. Q later said, "I had never done a day of martial arts in my life when I started in the business. I couldn’t even touch my toes."
In 1998, she started her acting career in the TV drama House of the Dragon, which was a huge hit in Asia. In 2000, Q made her film debut as Anna in the horror film Model from Hell, and went on to star as an FBI agent Jane Quigley in the action thriller Gen-Y Cops the same year. Her appearance in Gen-Y Cops impressed Jackie Chan so much that she was cast in Manhattan Midnight and Rush Hour 2.
In 2002, she starred as martial artist assassin Charlene Ching in the action film Naked Weapon. In 2005, Q played Harmony in the German-Singaporean TV mini-series House of Harmony, opposite Fann Wong. The same year she also co-produced the animal treatment documentary Earthlings narrated by Joaquin Phoenix.
In 2006, she starred alongside Tom Cruise in Mission: Impossible III. She played Zhen, the only female member of the IMF team. In 2007, she appeared as Mai Linh in the Bruce Willis movie Live Free or Die Hard, the fourth film in the Die Hard series, and as Maggie in Balls of Fury.
In 2008, Q played fictional Cao Ying, a granddaughter of the warlord Cao Cao in Three Kingdoms: Resurrection of the Dragon, her first ancient Chinese costume performance. That same year, she also appeared in the drama/thriller movie Deception starring Ewan McGregor and Hugh Jackman, as Tina, an investment banker who introduced Jackman's character to an exclusive anonymous sex club list.
Q also stars in the video game in the Need for Speed franchise Need for Speed: Undercover, as the seductive lead character, federal agent Chase Linh, who is the player's only contact to the Tri-City Police.
In 2010, she became the lead character, an assassin gone rogue, on the new CW series, Nikita, a revamp of the movie/TV title