Regan was born in Halifax, Nova Scotia, the youngest in a family of six. Regan is the daughter of former Nova Scotian premier Gerald Regan and sister of former federal Minister of Fisheries and Oceans Geoff Regan and Live at Five's Nancy Regan. She was first attracted to the art of ballet and studied professionally until she sustained an injury at 15 that forced her to quit. She went on to study at McGill University in Montreal where she found herself attracted to theater. She decided to move to New York City in her final year and completed her degree at the New School University.

A combination of acting and modeling skills sent Regan on a quick path to film with her first role in M. Night Shyamalan's Unbreakable. She landed her first starring role in Robert Harmon's They and displayed great skill and ability to carry a film on her own that has been earning her roles in television and film ever since.

Regan won an award for her role in My Little Eye at the 22nd Annual Atlantic Film Festival which her father accepted. She speaks French and Italian.