Harkin was born in Ballintogher, County Sligo in 1953. She is a graduate of University College Dublin with a Bachelor of Science degree in geology. She worked as a teacher of mathematics in a secondary school in Sligo town for 23 years.
She lived in Manorhamilton, County Leitrim with her husband, Seán Harkin, where he ran a grocery business until his death in 1996.
After her husband"s death, Harkin and her two sons moved to Sligo town where they now live.