Naseby, a village of Northamptonshire, England, 12 m. N. N. W. of Northampton, where was fought a decisive battle between Charles I. and the parliamentary forces under Fairfax, June 14, 1645. After the capture of Leicester by the royal army, Fairfax, who was besieging Oxford, marched into Northamptonshire. The two armies, about equal in number, confronted each other on the morning of June 14, the parliamentarians occupying a strong position near Naseby, and the king's troops being drawn up one mile south of Harborough. The royal centre was commanded by the king in person, the right wing by Prince Rupert, and the left by Sir Marmaduke Langdale. Fairfax, supported by Skippon, commanded the centre of his army, with Cromwell on his right wing and Ireton on his left. The royalists made the attack, and Rupert with his cavaliers charged with such fury upon Ireton that his wing was broken and put to flight. Instead of supporting his royal kinsman, Rupert detached himself from the main battle to pursue the fugitives. The royal centre maintained an obstinate contest till Cromwell, having routed the forces of Sir Marmaduke Langdale, fell suddenly upon its rear, when, unsupported by either of its wings, it almost immediately surrendered.

One regiment alone held out for the king, but was finally broken by repeated charges. At this moment Rupert returned from his needless pursuit of Ireton's troops, with his men and horses exhausted and the time for effective aid gone by. The king saved himself only by a precipitate flight. The royalists lost 800 killed and 4,500 prisoners, besides their artillery and ammunition; the parliamentarians had 1,000 killed. A number of private letters between Charles and his queen, subsequently published under the title of "The King's Cabinet Opened," also fell into the hands of the victors.