March 1682, made arrangements for Renwick to pursue his theological studies there, with a view to ordination. He spent a session at the university of Groningen. His ordination was promoted by the interest of Sir Robert Hamilton [q. v.] with Brakel, a Dutch divine. Renwick objected to subscribe the Dutch formularies as inconsistent with the covenant, and was allowed to substitute a subscription to the Westminster confession and catechism. His ordination certificate is dated 9 April 1683; a day later a remonstrance reached Groningen from the Scottish ministers of Rotterdam. On 10 May he received commendatory letters from the Groningen classis, and proceeded to Briel, to embark for the return voyage. He abandoned the first ship, on which he had taken passage, on account of ‘profane passengers’ pressing him to drink the king's health, and transferred himself to a vessel bound for Ireland. After some adventures he reached Dublin, where he found the nonconformist ministers very indifferent to his cause. Proceeding by sea to Scotland, he at once entered on his ministry there. His first sermon (September 1683) was in a meeting at Darmead Moss in the parish of Cambusnethan, Lanarkshire. He soon became noted as a field-preacher, and was proclaimed a rebel by the Scottish privy council. Though his fame spread, his position was variously misconstrued, some charging him with ‘the delirious and detestable blasphemies of Gib,’ the reference being to John Gib, shipmaster of Borrowstounness, Linlithgowshire, who, in April 1681, had started a semi-mystical sect of ‘sweet singers.’ Occasionally Renwick and his followers crept into churches by night and held their meetings. In 1684 efforts were made to apprehend him. In July he was nearly taken by a party of dragoons, but escaped with the loss of his papers. Letters of intercommuning (interdiction) were issued against him on 24 Sept. His followers hereupon urged the defiant measure of a new declaration, to which Renwick was at first averse. But in October he drew up ‘the Apologetical Declaration’ which, by concerted action, was affixed to a number of market crosses and church doors on 8 Nov. 1684. It claimed the right of dealing with the agents of authority as enemies of God, and ‘murdering beasts of prey.’ Two gentlemen of the king's lifeguards having been slain in an onset upon a field-meeting, the privy council ordered the death penalty for all who refused to disown this declaration on oath. The Scottish parliament, in April 1685, passed a statute making any acknowledgment of the covenant an act of treason. This led to the second Sanquhar declaration, promulgated by Renwick and his followers on 28 May 1685.
Renwick refused to join the insurrection of 1685 under Archibald Campbell, ninth earl of Argyll [q. v.] He was in sympathy with its object, but held aloof from a movement not distinctly put on the basis of the covenant. Hence he alienated many of his own party. His old friend, Sir Alexander Gordon, then a prisoner at Blackness, turned against him. He was viewed as a man who would only act by himself. Robert Cathcart, a Wigtonshire covenanter, protested against him; Alexander Peden [q. v.] was estranged from him, though they were reconciled on Peden's deathbed; Henry Erskine (1624–1696) [q. v.] peremptorily rejected his overtures. He found associates in David Houston, a turbulent Irish covenanter (see Reid, ed. Killen, 1867, ii. 328 sq.), and Alexander Shields [q. v.], his biographer.
James II's Scottish proclamations of indulgence (12 Feb. and 28 June 1687) gave full liberty for presbyterians to assemble for their worship in meeting-houses or private residences, on condition of registration and taking an oath of allegiance. Field conventicles were still prohibited. The conditions were satisfactory to all but Renwick and his followers, who would acknowledge no royal prerogative of dispensation, and insisted on maintaining their field-meetings. On 5 Oct. a proclamation ordered the utmost severity against such meetings; and on 18 Oct. a reward of 100l. was offered to any one who would deliver up Renwick, dead or alive. His friends must have been very faithful to him, for he made his way about the country, and, narrowly escaping arrest at Peebles, reached Edinburgh, where he lodged a protest against the indulgence with Hugh Kennedy, moderator of the Edinburgh presbytery, and afterwards got it promulgated. At the end of the year he preached for several Sundays in Fifeshire; on 29 Jan. 1688 he preached for the last time at Borrowstounness. Returning to Edinburgh, he lodged on the night of 31 Jan. at a smuggler's receiving house on the Castlehill. A customs officer, John Justice, who was watching the house, heard him at family prayer, and suspected who it was. Next morning (1 Feb.) Justice surprised him and endeavoured to effect his arrest. Renwick defended himself with a pistol, and got away to the Castlewynd in the Cowgate, where he was seized and taken to the Tolbooth. Graham, the captain of the guard, struck with his slight build, small stature, and youthful look, exclaimed: ‘What, is this the boy Renwick