She is the lead singer, keyboardist and songwriter of the rock band Metric and a member of the musical collective Broken Social Scene.

[4] She is the daughter of Canadian poet Paul Haines; her mother founded a school for under-privileged children in India.

Haines grew up in a house rich with experimental art and musical expression and her early influences included Carla Bley, Robert Wyatt, and PJ Harvey.

In 1996, she distributed a limited-edition album entitled Cut in Half and Also Double that included songs written and recorded during her student years.

[7] Haines met James Shaw in Toronto in 1997 and began performing as a duo called "Mainstream".

The band, appearing as themselves, performed their song "Dead Disco" and had minor speaking roles in a backstage scene.

[27] As secondary synthesizer, she played a Kawai MP9000,[28] which was replaced by E-mu's PK-6 Proteus Keys in 2003, and was followed by the Clavia Nord Wave in 2012.

[29][30] In August 2013, Haines became involved with FLEET4HEARme, a collaboration with Fleet Jewelry and HearMe, an organization that aims to increase children's access to music programs in public schools.

Metric is active in the international advocacy organization Global Citizen, and Haines is involved with its girls and women issues campaign #SheDecides.