The First Battle of Newbury was a battle of the First English Civil War that was fought on 20 September 1643 between a Royalist army, under the personal command of King Charles, and a Parliamentarian force led by the Earl of Essex. Following a year of Royalist successes in which they took Banbury, Oxford and Reading without conflict before storming Bristol, the Parliamentarians were left without an effective army in the west of England. When Charles laid siege to Gloucester, Parliament was forced to muster a force under Essex with which to beat Charles' forces off. After a long march, Essex surprised the Royalists and forced them away from Gloucester before beginning a retreat to London. Charles rallied his forces and pursued Essex, overtaking the Parliamentarian army at Newbury and forcing them to march past the Royalist force to continue their retreat.

Reasons for the Royalist failure to defeat the Parliamentarians include shortage of ammunition, the relative lack of professionalism of their soldiers and the tactics of Essex, who compensated "for his much lamented paucity of cavalry by tactical ingenuity and firepower", countering Rupert's cavalry by driving them off with mass infantry formations. Although the numbers of casualties were relatively small (1,300 Royalists and 1,200 Parliamentarians), historians who have studied the battle consider it to be one of the most crucial of the First English Civil War, marking the high point of the Royalist advance and leading to the signing of the Solemn League and Covenant, which brought the Scottish Covenanters into the war on the side of Parliament and led to the eventual victory of the Parliamentarian cause.