Sheena Duncan was born in Johannesburg in 1932. She was educated at Roedean School in Johannesburg and in the 1950s studied at the Edinburgh College of Domestic Science in Scotland. After qualifying as a Domestic Science teacher she moved to Rhodesia (Zimbabwe). She returned to South Africa eight years later and worked for the Social Welfare Department of the Johannesburg City Council as a home economics officer.

Sheena Duncan was the daughter of the late Jean Sinclair, a founder member of Black Sash, a womens organization working for human rights. She joined the Black Sash in 1963, working tirelessly against inhumane laws and the effects of the apartheid on ordinary South Africans, especially women. She held various positions within the organization including regional chairperson and editor of the Sash Magazine. In 1975 she became the national president of Black Sash taking over from her mother who had retired the same year from this position. She wrote several articles, booklets, pamphlets, speeches, especially on issues such as forced removals and pass laws. In 1970 Sheena Duncan joined the Anglican Churchs Challenge Group, a movement that sought to end racism within the church. She also represented the Anglican Church on the South African Council of Churches (SACC) Justice and Reconciliation Division. She became and still is the Honorary Life Vice President of the SACC as well as chair and patron of Gun-Free South Africa and of the Black Sash.

In 1986 she received the Liberal International Prize for Freedom for her outstanding contribution to human rights and political freedom. She has also been awarded honorary doctorates in Law by the University of the Witwatersrand in 1990, the University of Cape Town in 1991 and the University of Natal in 1995. Sheena Duncan has had an outstanding career as a public figure involved in the struggle to promote social justice and human rights. She was a fervent activist for these causes. Sheena Duncan died in 2010.