Attended Camden High School in Camden, New South Wales between 1971–1976 and was School Captain in her final year.
Heather took the leading role of Elvira in the 1976 school drama production of Noël Coward's Hay Fever.
Other television series include: Five Mile Creek, the miniseries Bodyline (1984), I Can't Get Started (1985), Land Of Hope (1986) as Helen Davies (10 episodes), Embassy and A Country Practice. In 1998, she starred in the miniseries drama The Day of the Roses, in which she played a victim of the 1977 Granville railway disaster. She also appeared in episode 1.5 of Rake (2010).
Mitchell starred in Cody I: A Family Affair (1994), Cody II: Bad Love (1994), Cody III: The Tipoff (1994), Cody VI: The Wrong Stuff (1994).
Mitchell is well known for her performance as "Ashka" in the Australian/Polish co-productions of Spellbinder, and Spellbinder: Land of the Dragon Lord. The series was a popular children's fantasy program first broadcast in 1995.
Theatre productions include The White Devil (August 2000), Bye Bye Birdie (March 2001). Mitchell played Hamlet's mother Gertrude in Bell Shakespeare's Hamlet at the Playhouse, Arts Centre, Melbourne, in July 2008. In July to August 2011 she appeared in the Belvoir St Theatre's, Neighbourhood Watch. In 2017 she played Edward and Betty in the Sydney Theatre Company production of Caryl Churchill's Cloud Nine directed by Kip Williams.
She appeared in the 2006 Australian tele-movie The Society Murders as Sally Wales, starring alongside Georgie Parker. Other tele-movies she has appeared in include Emerald Falls.
