Mary Helen MacKillop RSJ (15 January 1842 – 8 August 1909) was an Australian nun who has been declared a saint by the Catholic Church, as St Mary of the Cross.
Of Scottish descent, she was born in Melbourne but is best known for her activities in South Australia.
Together with the Reverend Julian Tenison Woods, she founded the Sisters of St Joseph of the Sacred Heart (the Josephites), a congregation of religious sisters that established a number of schools and welfare institutions throughout Australia and New Zealand, with an emphasis on education for the rural poor.
The process to have MacKillop declared a saint began in the 1920s, and she was beatified in January 1995 by Pope John Paul II.
Pope Benedict XVI prayed at her tomb during his visit to Sydney for World Youth Day 2008 and in December 2009 approved the Catholic Church's recognition of a second miracle attributed to her intercession.
She was canonised on 17 October 2010, during a public ceremony in St Peter's Square at the Vatican.
She is the first Australian to be recognised by the Catholic Church as a saint.