William Mitchell (20 November 1803 – 3 August 1870) was a Church of England priest who was the first ordained person to provide religious services in the Swan Valley area of the Swan River Colony. He worked in the Swan Parish for over 20 years before moving to Perth to take up a position working with convicts and prisoners in the Perth Gaol in Beaufort Street.
Mitchell was the first rector of the Swan Parish, an area which extended north to Gingin and Chittering and east to Toodyay and York. The southern boundary included Guildford and Midland.
Mitchell was born in the County of Monaghan, Ireland. He and his three brothers were orphaned as young children after his father, William Mitchell, was reputedly killed in Dublin riots (his mother's cause and date of death is uncertain). The boys grew up in "Stackallen House" in County Meath, Republic of Ireland, the home of an uncle and under the care of a nurse. In 1810 he moved to live with his grandfather, Blayney Owen Mitchell, in Dublin who was a well-known attorney. While living there he was apprenticed to an apothecary for about one year and studied at Trinity College, Dublin before deciding to become a missionary.
Missionary training was done at Olney, Buckinghamshire and at the Church Missionary House in Salisbury Square, London which was run by the Church Missionary Society from where he was ordained as a priest by the Bishop of London in 1825. In January 1826 he married Mary Anne Holmes. They left Ireland for a missionary position in India, where two daughters and a son were born in 1826, 1828 and 1829.