 He was born Philip Ellis, the son of John Ellis, Rector of Waddesdon, Buckinghamshire, a descendant of the Ellis family of Kiddall Hall, Yorkshire, and Susannah Welbore.Of six brothers, John, the eldest, became Under-Secretary of State to William III of England; William, a Jacobite Protestant, was Secretary of State of James II of England in exile; Welbore became Protestant bishop of Kildare and afterwards of Bishop of Meath, Ireland; Samuel was Marshal of King's Bench; and Charles an Anglican clergyman.Ellis, while still a Westminster schoolboy, was converted to the Catholic faith from his Anglicanism, and when 18 years old went to St Gregory Priory in Douai, France, where he was received as a monk, taking the religious name of Michael, making his religious profession on 30 November 1670.