Page was born and raised in Halifax, Nova Scotia, the daughter of Martha Philpotts, a teacher, and Dennis Page, a graphic designer. She attended the Halifax Grammar School until grade 10, spent some time at Queen Elizabeth High School, and graduated from the Shambhala School in 2005. She also spent two years studying in the Interact Program at Vaughan Road Academy in Toronto, Ontario. Growing up, Page enjoyed playing with action figures and climbing trees.

Page began acting at age 10, appearing in the telefilm Pit Pony, which would later spin-off a television series. This led to roles in a number of small Canadian films and television series—notably playing Treena Lahey in Season 2 of Trailer Park Boys. At 16, she was cast in an independent film shot in Europe, Mouth to Mouth.

Page next starred in Smart People, which premiered at the 2008 Sundance Film Festival and received a wide release on April 11, 2008. Page has roles in three films unreleased as of January 2008: An American Crime, which premiered at the 2007 Sundance Film Festival; The Tracey Fragments, which is scheduled for a U.S. release in early 2008; and The Stone Angel. Page is also attached to star in Peter Stebbings' The Defender as well as Jack and Diane opposite Olivia Thirlby, with whom she co-starred in Juno.

Page hosted Saturday Night Live on March 1, 2008 with musical guest Wilco (special appearances by Hillary Rodham Clinton, Rudolph Giuliani and Vincent D'Onofrio.) For her traditional opening monologue, she mocked the stylized dialogue of the movie Juno with cast member Andy Samberg, who impersonated Juno screenwriter Diablo Cody Page's SNL characters included Miley Cyrus Peter Pan, Virginia Hastings' stepdaughter, and a young woman named Marty who realizes she is a lesbian after attending a Melissa Etheridgeconcert.

As of January 2008, Page resides in her hometown of Halifax. Page mentioned in an interview with Barbara Waltersthat she sleepwalks and hallucinates when she sleeps. In an interview by Drew Barrymore for Interview Magazine (March 2008) Page said that she has a dog named Patti, whom she named after one of her idols, Patti Smith.