Reynolds, Sir John (1625–57), Cromwellian soldier, was third son of Sir James Reynolds of Castle Camps, Cambridgeshire, England; his mother was a daughter of Sir Robert Mordaunt. Educated at Cambridge and at the Middle Temple in London, Reynolds used his family's East Anglian connections to gain a commission as captain of horse in Oliver Cromwell's (qv) regiment in 1645. He distinguished himself in the storming of Bridgwater (July 1645), and was noted as ‘one of the greatest favourites’ of Cromwell in his own regiment (C. H. Firth (ed.), Clarke papers, i, 22). In 1647 Reynolds was active in the army council meetings at Saffron Walden, Essex, and organised resistance against the plan to ship New Model regiments to Ireland. But his radical views soon raised doubts as to his loyalty to the high command, and in May 1648 he was sentenced to three months in prison and cashiered for his support of the Levellers. This was a sobering experience, which prompted Reynolds to abandon the Levellers (who denounced him as a ‘turncoat’) in late 1648, and accept the rank of colonel, commanding a new regiment intended for Ireland. The test came in April and May 1649, when his regiment mutinied and ‘declared for the Levellers’ (The Kingdomes Faithfull Scout, no. 15 (4–11 May 1649), 119), but Reynolds proved his loyalty, suppressing dissent in his own regiment and helping to crush the main Leveller force at Burford, Oxfordshire.
Reynolds arrived in Dublin, as part of the Cromwellian advance-guard, in time to support Michael Jones's (qv) victory at Rathmines in August 1649. He served at Drogheda and Wexford, and in December took the stronghold of Carrick-on-Suir in Co. Tipperary. In 1650–51 he fought in Kerry, Limerick, and Connacht, being promoted to commissary-general (April 1651); in 1652 he negotiated articles with Irish commanders surrendering in the midlands; and in 1653 commanded the forces that captured the Aran Islands and Inishbofin. As a reward for his service, Reynolds was granted lands in Carbery, Co. Cork, and the old Butler estates at Carrick-on-Suir. In 1654 he was double-returned to the union parliament at Westminster for Tipperary and Waterford and also Galway and Mayo, and elected to sit for the latter. After the parliamentary session he remained in England, helped to put down royalist unrest in the midlands, and was knighted by Cromwell in June 1655.
At this time Reynolds was betrothed to Sarah, daughter of Sir Francis Russell, and sister-in-law of the new acting-governor of Ireland, Henry Cromwell (qv). Reynolds became one of Henry Cromwell's closest allies, turning his back on the more radical of his army colleagues, and advocating instead a broad political settlement embracing the Old Protestants as well as the new arrivals. During 1656 Reynolds was Henry Cromwell's agent at the protector's court, working for ‘the sober settlement of Ireland’ (BL, Lansdowne MS 821, f. 192), and fending off the attacks of John Hewson (d. 1662) and other malcontents in the Irish army. When a new parliament was called in July 1656, Reynolds was supported as candidate for Cambridgeshire by his prospective father-in-law, Sir Francis Russell, but he chose instead to sit as MP for Tipperary and Waterford. During the parliament Reynolds once again acted as Henry Cromwell's agent, working with the other Irish MPs in matters of domestic concern. He was also a key figure in the kingship debates, supporting Lord Broghill (qv) and his allies in their efforts to force through the new constitution, and sending detailed accounts of the progress of reform to Henry Cromwell in Dublin.
In April 1657 Reynolds was appointed captain-general of 6,000 troops to be sent to France to support the war against Spain in Flanders. He married Sarah Russell in early May, but within a week of the wedding had sailed to France. In the next few months he proved his worth as a commander, capturing the fort at Mardyke (September), and holding it against ferocious attempts by the Spaniards to recapture it. After lobbying by his new father-in-law and others, he was at last allowed to return home on leave, setting sail in a small boat on 5 December 1657 in order to meet a warship off the French coast. Missing their contact, the boat crossed towards England in the teeth of a gale, and sank on Goodwin Sands with the loss of all hands. Reynolds's death was a catastrophe not only for his family but also for those who hoped for further reform in England and Ireland. In John Thurloe's words, ‘this loss is exceeding sad and very great blow to us’ (Thurloe state papers, vi, 676).