Britt Irvin was born Brittney Elizabeth Irvin in Vancouver, British Columbia, Canada, and raised in Surrey, British Columbia. She began dancing ballet and singing in festivals starting around 1990 when she was 6 years old. She worked on two musicals at age 10, Show Boat and A Christmas Carol, did voice work in the television series "Nilus the Sandman", and did work in several television commercials between productions, many of which aired in the United States as well as Canada.

In 1996, Irvin appeared in the films Panic in the Skies! and The Angel of Pennsylvania Avenue. In 1998 she appeared in the TV series Little Men on Canada's CTV network, which lasted two seasons. Between 1998 and 2000 Irvin also played guest roles on Sleepwalkers, Night Man, Stargate SG-1, and The Outer Limits. In 2000 she played Laurel Everett in the TV movie Angels in the Infield which also starred Patrick Warburton and David Alan Grier. Also in 2000, she played the role of Maxine Bronty in Quarantine.

In 2000 Irvin acted in So Weird. In 2002 Irvin played a red-wine-loving kleptomaniac named Amy in the MTV movie Wasted and played a role in The Outer Limits again in 2003, the same year she appeared in National Lampoon's Thanksgiving Family Reunion with Judge Reinhold and Penelope Ann Miller. Also, in 2003, she portrayed the late Dana Plato in the NBC TV movie Diff'rent Strokes: The Unauthorized Biography.

Irvin released a demo music album in 2003. She has been known to give live performances in Vancouver and Los Angeles. Her music has never been mass-released, but some of the tracks have been found at sites like YouTube.

She played the single teenage mother Paige Leckie in the fourth season of Edgemont in 2004, but left the series after just one season in order to fulfill other commitments. Also in 2004 she played "Maggie" in the movie Jack.

Her works have included the 2005 film Reefer Madness which is based on the 2003 musical, (though she only appeared in one scene), the 2005 TV movie Absolute Zero with Jeff Fahey and Erika Eleniak, the 2007 film Hot Rod starring Andy Samberg, and her recent appearance playing the love interest of Kevin Zegers' character in Normal, which was also released in 2007.

Irvin also provided the voice of the character Ursula in the 2007 George of the Jungle cartoon series which aired on the Cartoon Network, making her the first (and currently only) person ever to voice a cartoon character in a series remake, where the character had originally been voiced by June Foray in the original. Foray had originally voiced the character Ursula in the original George of the Jungle series from the 1960s – though the character is significantly different in the 2007 series than in the 1967 series. The series aired for only one season.

She was nominated for a Leo Award in 2008 for her performance in Normal.

She appeared in the first three episodes of ABC's remake of the 1980s science fiction miniseries V, which premiered on ABC on November 3, 2009, as well as the first episode of Life UneXpected, which premiered in February 2010 on The CW. Irvin portrayed Stargirl in the Smallville episodes "Absolute Justice", "Salvation", "Icarus" and "Prophecy". Her most recent credit is as Kathy Patton in Freshman Father, a Hallmark Channel movie where she portrays a prom queen turned young mother suffering from severe post-partum depression. In 2010, she plays in Barbie: A Fashion Fairy Tale and Barbie: A Fairy Secret, as the voice of Raquelle.

She co-starred in Michael Sucsy's 2012 film The Vow, which starred Rachel McAdams and Channing Tatum, and also included her former Little Men and Angels in the Infield co-star Rachel Skarsten in the cast.