He was the son of Cornelius van Mildert, a gin distiller, and his wife Martha née Hill. Cornelius Van Mildert was the great-grandson of an Amsterdam merchant who migrated to London around 1670, Martha the daughter of William Hill of Vauxhall, Surrey, merchant and financier.
William van Mildert was educated at Street Saviour"s Grammar School, Merchant Taylors" School (then in London) and the Queen"s College, Oxford.
His name survives in Van Mildert College, founded in 1965 and the Van Mildert Professor of Divinity. Loosely attached to the high church party, he was appointed Bishop of Llandaff from 1819 to 1826, a post which he held in commendam with the Deanery of Street Paul"s between 1820 and 1826, when he was translated to Durham. Prior to this, he had been rector of the church of Saint Mary-le-Bow in London and Regius Professor of Divinity at Oxford, where he gave the Bampton Lectures for 1814.
Van Mildert is often described as a "stormy petrel" on account of his outspoken expression of his views.
As Bishop of Llandaff he broke with the practice of his predecessors and actually resided in the diocese. As the bishop"s palace had fallen to ruin, he rented Coldbrook House bear Abergavenny.
During his time in Llandaff, he gained a reputation as "a conscientious diocesan". As part of the University of Durham"s foundation, behind which he was the driving force, he gave Durham Castle to the University, where it became the home of University College.
Auckland Castle therefore became the sole residence of the Bishop of Durham.
In addition, he donated a large number of buildings on Palace Green, between the Castle and the Cathedral. These are currently in use by various departments of the University (principally law, music and a small portion of the University Library).
