Soon after the Restoration of 1660, he was invited to Ireland by Jeremy Taylor, ordained deacon and priest on 7 May 1661, and made dean of Connor in August.
[2] On 20 October 1663, preaching at Newtownards at the funeral of Hugh Montgomery, 1st Earl of Mount Alexander, Rust remarked, "New presbyter is but old priest writ large"; John Milton's sonnet containing the same line was not published till 1673.
In succession to Taylor, Rust was appointed bishop of Dromore by patent in November 1667, and consecrated in Christ Church, Dublin, on 15 December.
He died of fever in the prime of life in December 1670, and was buried in the choir of Dromore Cathedral in the same vault with his friend Taylor.
[2] In 1655 Rust delivered a Latin discourse in Great St. Mary's, Cambridge, in answer to Pontius Pilate's question "What is Truth?"