Educated at Sacré Cœur School, Glen Iris, Melbourne and at the University of Melbourne, Marie O'Brien qualified as a lawyer. She married James "Jim" Tehan in 1963 and settled in regional Victoria. They had six children. She established her own legal practice in Mansfield in 1970.
Tehan was elected to the Victorian Parliament in 1987 and retired from Parliament in 1999. Representing the Liberal Party, Marie Tehan served in both Houses of the Victorian Parliament. She was the member for Central Highlands in the Legislative Council from 1987 to 1992 and for Seymour in the Legislative Assembly from 1992 to 1999. As a minister in the Kennett Liberal government, she held the portfolios of Minister for Health from 1992 to 1996 and Minister for Conservation and Land Management from 1996 to 1999.