Quigley attended Mililani Waena Elementary School and Wheeler Intermediate School. She then attended Mililani High School, where she was on the cross country, track and field, and swim teams. She won the title of “Best Body” senior year, and graduated in 1997. She won an athletics scholarship to a private university and intended to study veterinary science. Quigley’s family was unable to assist her financially. She left Hawaii at the end of one school year in hopes of earning enough money so that she could start by the beginning of the following one.

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 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 2004 she co-starred with Kelly Hu, Russell Wong and other Asian-American actors in a 30-second PSA produced by Mark Allen for CAUSE USA (Center for Asian Americans United for Self Empowerment), The Least Likely, encouraging Asian and Pacific Islander Americans to register and vote. 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 Q made her Hollywood breakthrough as co-star in Mission: Impossible III alongside Tom Cruise. 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 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 2007, she lived in Studio City, Los Angeles, California with her two (at one point, eight) rescued dogs. She also has a house in Pound Ridge, New York.

Q is outspoken on the subject of animal rights and has taken part in PETA Asia’s campaigns promoting vegetarianism. A vegetarian for many years, she has said that giving up meat was one of the most rewarding decisions she has ever made. “I feel better, I have more energy, on, and off the set, and I have the satisfaction of knowing that I’m doing something to help stop animal suffering.” In 2008, Maggie Q was named PETA Asia-Pacific’s “Person of the Year.” The same year, the organization also listed Q as one of the “Best-Dressed Celebrities” of 2008. She has since taken the step to cut all animal products from her diet by becoming a vegan. PETA named her one of three “Sexiest Vegans” of 2017. Maggie Q is currently an ambassador for Animals Asia Foundation.

In 2010, Q became the lead character, an assassin gone rogue, on the CW series Nikita, based on the 1990 French film of the same name. Since the premiere of Nikita, Q has been incorrectly described as the first Asian American series lead in an American television drama; actress Anna May Wong is the first Asian American series lead of an American television series with her show The Gallery of Madame Liu-Tsong which aired 1951. Q received mostly positive reviews for her role in the series. The character was included in TV Guide’s lists of “TV’s Sexiest Crime Fighters” and “TV’s Toughest Ladies”.

She has five tattoos: a cross on her right forearm, Tibetan script and a little triangle on her left forearm, and a Zulu proverb on her side “umuntu ngumuntu ngabantu”, which means “a person’s character is made by the collective”. She has one of a phoenix on her left hip, which she has had to conceal for most of her roles except Nikita. Q has suffered temporary hearing loss in her right ear after her eardrum was damaged during an explosive stunt in 2010.

In 2014, Q played the role of Dauntless faction member Tori Wu, in the film Divergent, the adaptation of the same-titled novel. Q reprised her role in the sequel to Divergent, The Divergent Series: Insurgent, which began filming on May 27, 2014 and was released on March 20, 2015. She also starred in the CBS drama series Stalker by Kevin Williamson as Detective Beth Davis along with Dylan McDermott and Mariana Klaveno. The series premiered on October 1, 2014 for the 2014–15 fall television season. The series was ordered for a full season on October 27, 2014. The series however was canceled after one season, leaving the show on a cliffhanger. In October 2013, Q started filming for A Conspiracy on Jekyll Island, starring alongside Frank Grillo, AnnaSophia Robb, Dianna Agron, John Leguizamo, Ed Westwick, Mary McCormack, Christopher McDonald and Minnie Driver. The film is directed by Aram Rappaport and produced by Hilary Shor, Atit Shah and Aaron Becker. Jekyll Island is set to release in 2016.

Q dated Los Angeles-based businessman Paul Alfonso from 2009 until 2010. After meeting her Stalker co-star Dylan McDermott on-set in early 2014, their engagement was announced on January 14, 2015. The couple stated in 2017 that they were not in any rush to have an actual wedding ceremony. In February 2019, after a four-year engagement, the couple split.

She reprised her role in The Divergent Series: Allegiant, the third installment of the Divergent series, which was released on March 18, 2016. In February 2016, it was announced that she would co-star opposite Kiefer Sutherland in the ABC drama series Designated Survivor as Hannah Wells, a leading FBI agent. The show was renewed by Netflix for a third and final season, which was released on June 7, 2019.