She is best known for her roles as Lieutenant Margaret "Racetrack" Edmondson in Battlestar Galactica and as Kathryn MacLaren in the TV series Travelers.

Cairns appeared in Robson Arms before winning a recurring role as Jenna in Godiva's, for which she received a Leo Award nomination in 2006 for Best Supporting Performance by a Female in a Dramatic Series.

During BSG's season three Cairns also played Emily Hollander on the ABC Family series Kyle XY and appeared in Sanctuary.

In 2018, she co-starred in the film Diminuendo opposite Richard Hatch, her friend from the BSG reboot.

Her niece has Transverse myelitis, with Cairns' starting a Gofundme page to raise money for her medical treatment.