Doig's exotic appearance stems from her mixed heritage - Irish and Scottish descent on her father's side, Filipina on her mother's. She was born and raised in Toronto, Ontario, where her family held season tickets to their local theatre, and caught the acting bug at the age of nine, after seeing a production of Porgy and Bess. At the age of sixteen, she enrolled in a modelling course and was immediately picked up by an agent. She did commercials and modelling work, before dropping out of high school during her final year to pursue an acting career. She worked on stage productions of Romeo and Juliet and Arsenic and Old Lace while auditioning for film and television roles.

She had a small role on Gene Roddenberry's Earth: Final Conflict.

Her first significant role was on William Shatner's series TekWar as the character "Cowgirl", a specialist in tracking and obtaining information from the net. Doig recalls the time she heard the news of this role: "I walked out of the audition absolutely convinced I had blown it, and then my agent called to tell me I got the part. I was leaping around my parents' house and screaming at the top of my lungs. I knew then I'd chosen the right profession and I've never looked back since."

Doig landed the role of Tina Backus on the short-lived series CI5: The New Professionals in 1998, and finally burst into the spotlight with her role as the title character on the sci-fi series Andromeda. More recently, she has expanded into significant feature film roles, including the female lead in Jason X (2001). Doig has also shot several episodes for the ninth season of Stargate SG-1, in a recurring guest role as the team's new doctor, Carolyn Lam. She also has a recurring role as college professor Wendy Paulson in the second season of The 4400.

When not performing, Doig enjoys reading, rollerblading and playing RPG video games and Dungeons and Dragons. Her cousin is actor Rey-Phillip Santos. On 2 August 2003 she married fellow actor Michael Shanks. The two welcomed a daughter, Mia Tabitha, on 13 September 2004. She was followed in March 2006 by another child, this time a boy named Samuel David. The family divide their time between Toronto and Vancouver, the centre of the Canadian film industry, with plans to move to Los Angeles in the near future.