The eldest son of Isaac Milles the elder, he was born at Barley, Hertfordshire, on 19 June 1671. He matriculated at Wadham College, Oxford, on 12 March 1689, was exhibitioner of the college in 1691–2, and graduated B.A. in 1692, M.A. in 1695, and B.D. in 1704.[2]
Having been ordained by Bishop John Hough, he became chaplain of Christ Church, Oxford, in 1694, and was from 1695 to 1707 vice-principal of St Edmund Hall. He was appointed Regius Professor of Greek in 1705–1707. In April 1707 he went to Ireland as chaplain to the new lord-lieutenant, Thomas Herbert, 8th Earl of Pembroke, and on 11 March 1708 was appointed bishop of Waterford and Lismore. He was consecrated in St Patrick's Cathedral, Dublin, on 18 April.[2]
Milles's appointment was unpopular in Ireland, on account of his High Church views. As bishop, Milles took trouble to restore churches. After an episcopate of more than thirty years he died of the stone at Waterford on 13 May 1740, and was buried in Waterford Cathedral. He was unmarried, and left his property to his nephew Rev. Jeremiah Milles (1714-1784), Dean of Exeter.[2]
