Poyntz was originally apprenticed to a London tradesman, but, being ill-treated by his master, he took service as a mercenary soldier in Holland, and in the Thirty Years' War.

He changed sides and fought as a captain in Wallenstein's army in the service of Emperor Ferdinand II at the Battle of Lützen in 1632.

[6] He was ordered after Battle of Naseby (14 June 1645) to follow the movements of King Charles I, and succeeded in forcing him to an engagement at Rowton Heath, near Chester, on 24 September.

Poyntz was seized by the agitators on 8 July 1647 and sent a prisoner to Fairfax's headquarters, charged with endeavouring to embroil the kingdom in a new war.

[15] He was released by Fairfax on parole; but the latter, who now became commander-in-chief of all the land forces in the service of Parliament, appointed Colonel John Lambert to take command in the north.

[1] On 2 August Poyntz and other officers dispersed a body of citizens who brought to the common council a petition "praying that some means might be used for a composure".

[17] On the collapse of the resistance of London, Poyntz fled to Holland, publishing, in conjunction with Massey, a declaration "showing the true grounds and reasons that induced them to depart from the city, and for a while from the kingdom".

[18] On 14 May 1648 Poyntz wrote to the Speaker of the House of Commons from Amsterdam, begging that he might at least receive the two months' pay voted to his forces when they were disbanded.

[19] Receiving no answer to this or previous appeals, Poyntz in 1650 accompanied Lord Willoughby to the West Indies, and there became governor of the Leeward Islands, establishing himself on Saint Kitts.

[1] When Willoughby surrendered Barbados to the Parliamentary fleet under Sir George Ayscue, Poyntz found Saint Kitts untenable, and retired to Virginia.

[3] It is possible that he married his third wife while living abroad because in a letter to Speaker of the House of Commons, William Lenthall, in 1647 she mentions that "stranger in your kingdom" and signed her name as Elisabeth.