Born into a minor gentry family at Reigate in Surrey, Sydenham Poyntz was apprenticed to a London tradesman but ran away to become a mercenary soldier. He fought in the Dutch service, in the army of Count Mansfeld and was present at the battle of Breitenfeld in 1631, after which he changed sides and fought at the battles of Lützen and Nordlingen under the Imperial general Count Wallenstein. He wrote a memoir of his experiences in the European wars: the Relation of Sydenham Poyntz. He married three times whilst serving abroad. His first wife died in childbirth around 1633; his second wife and their child were killed by French soldiers; his third wife, Elizabeth, returned with him to England around 1644.
Poyntz took service with Parliament and replaced Major-General Lambert as commander of the Northern Association army in May 1645. He manoeuvred to block King Charles on his march to join Montrose in Scotland then defeated the King's cavalry at Rowton Heath near Chester in September 1645. After reducing several Royalist strongholds in Nottinghamshire, Poyntz initiated the final siege of Newark in November 1645, where he was joined by Lord Leven and the Covenanter army.
During the disputes between Parliament and the Army in 1647, Presbyterian MPs looked to Poyntz for support against the New Model Army. His dealings with the Presbyterians were regarded with suspicion by Fairfax and Cromwell, who suspected he was plotting to take the northern army over to the Scots in the event of an invasion. Agitators from the New Model Army infiltrated the Northern Association and discontented soldiers threatened to mutiny over arrears of pay. In July 1647, Poyntz was dragged from his lodgings at York by his mutinous troops and taken as a prisoner to Fairfax's headquarters at Reading. Although Fairfax liberated him immediately, Poyntz was replaced as commander of the Northern Association. He went to London where he became involved with Edward Massey and Sir William Waller in attempting to mobilise the City militia against the Independents and the New Model Army. Poyntz led the militia in a violent attack on a demonstration by civilian Independents in August 1647. He fled abroad when the Army marched into London a few days later.
During the Second Civil War, Poyntz supported the King's alliance with the Scottish Engagers. He was commissioned Major-General to the Presbyterian Lord Willoughby of Parham whom the Prince of Wales appointed commander of Royalist forces in East Anglia. With the defeat of the Engagers at the battle of Preston, however, the projected Royalist uprisings and invasions in England came to nothing. In 1650, Poyntz sailed with Lord Willoughby to the West Indies where they declared for the King in the English colonies. The Commonwealth responded by sending a force under General-at-Sea George Ayscue, who succeeded in quelling the Royalists in January 1652. Willoughby returned to England, but Poyntz's movements after this date are unknown. According to one account he fled to Virginia.
References:
D. N. Farr, Sydenham Poyntz , DNB, 1894