Mary Helen MacKillop RSJ (15 January 1842 – 8 August 1909), now formally known as St Mary of the Cross MacKillop, was an Australian nun who has been declared a saint by the Catholic Church. Of Scottish descent, she was born in Melbourne, but was 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 Australasia, with an emphasis on education for the rural poor.

With the process to have MacKillop declared a saint having begun in the 1920s, 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 and only Australian to be recognised by the Catholic Church as a saint.

Mary MacKillop is Australia's first and only Roman Catholic Saint.

Mary MacKillop may also refer to:

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