She was educated at Girton House Girls' Grammar School and received her LLB from the University of Adelaide in 1927, going on to practice as a barrister in Sydney and London.

She married Alan John Richmond Miller (died 1965) on 24 July 1930 at St. George's Anglican Church, Hobart.

During World War II, Mabel Miller served in the Women's Auxiliary Australian Air Force (WAAAF); from 1941 to 1944 she was stationed on airbases around Australia.

Miller decided to enter local politics when she heard there was mismanagement occurring in the Hobart City Council.

Dame Mabel Miller died on 30 December 1978, in a New Town, Tasmania nursing home,[3] aged 72, from undisclosed causes, and was cremated.