Mairi Petersen was born in Maclean on the north coast of New South Wales and completed her Primary Teacher's Certificate at Newcastle Teachers' College. Her first appointment was to Kellyville Primary School in the north west of Sydney. Subsequently she taught at Forest Lodge, Darlinghurst, Fort Street, Clovelly and Glenmore road, Paddington in the inner suburbs. Later she moved to the Illawarra area and taught at Mount Warrigal, Albion Park Rail and Shellharbour primary schools.
Mairi Petersen married (1) Robert Gould,( marriage dissolved) with whom she had a daughter, Natalie, and (2) George Petersen, MLA for Illawarra 1968-1988 (died 28 March 2000).

Together the Petersens ran an environmental radio programme on the community radio station 2 VOX-FM for eight years.
Mairi Petersen has travelled widely, particularly to third world countries, and was a member of the Cuba Work Brigade.
She has been an active member of Amnesty International for many years and has taken part in many other community activities. She and George Petersen were long time members of the Illawarra Folk Club and Mairi has sung with the Trade Union Choir.

She is active in the Illawarra section of the Australian Society for the Study of Labor History, and has been a member of the Council for Civil Liberties for many years.

Sources used to compile this entry: Mairi Petersen 21 October 2005; Ephemera on NSW State and local elections, Box 6, Mitchell Library collection, State Library of NSW, Sydney.