In 1629, by command of Charles I, he waited on William Laud, Archbishop of Canterbury, to explain the views of the Scottish hierarchy in reference to a Book of Common Prayer.
In 1630, Maxwell was in correspondence with Henry Leslie, then dean of Down, about the presbyterian irregularities of Robert Blair, and other Scottish clergymen who had migrated to the north of Ireland.
He carried to the court an account, derived from Leslie, of Blair's alleged teaching respecting physical convulsions as requisites of religious revival.
In conjunction with James Wedderburn, Bishop of Dunblane, he certainly had a chief hand in drawing up the new service-book for Scotland, subsequently revised by Laud, Juxon, and Wren.
In December 1637, in consequence of the opposition to the service-book, the privy council sent the lord high treasurer (John Stewart, 1st Earl of Traquair) to London for instructions.
The service-book was in use at Fortrose till 11 March 1638, when"certane scolleris cam pertlie in to the kirk and took wp thir haill seruice bookis, and careit them doun to the Ness with ane coill of fyre, thair to haue brynt them altogidder.
Maxwell was charged with bowing to the altar, wearing cope and rochet, using "the English liturgy" for the past two years in his house and cathedral, ordaining deacons, giving absolution, fasting on Friday, and travelling and card-playing on Sunday.
The day after the death (26 November 1639) of Archbishop John Spottiswood, Maxwell, in terms of the deceased primate's will, gave the manuscript of his history into the king's own hand at Whitehall.
In 1640, Maxwell went over to Ireland, where he was made D. D. by Trinity College, Dublin, and appointed on 12 October 1640, Bishop of Killala and Achonry by royal patent, in room of Archibald Adair, deprived 18 May for favouring the covenant.
Fleeing with his wife, three children, and neighbours, the company, numbering about a hundred, was attacked at the bridge of Shruel, County Mayo, when several were killed and the bishop stripped, wounded, and left for dead.
When the news reached him at Dublin of the surrender of Charles by the Scottish army (30 January 1647), he retired to his closet and was found dead on his knees on 14 February 1647.