The first Battle of Newbury took place on 20 September 1643 between Parliamentary forces under Robert Devereux, the Earl of Essex, and royalist forces under King Charles in person, accompanied by Prince Rupert and Sir Jacob Astley. The two sides were fairly evenly matched; Charles had about 8,000 infantry and 6,000 cavalry while Essex had 10,000 infantry and 4,000 cavalry. Both sides had about 20 artillery pieces.

Although the royalists had arrived at Newbury ahead of the Parliamentarians, Essex made better use of the ground, securing positions on a hill overlooking the battlefield. While the royalists succeeded in routing the Parliamentarian cavalry, they were unable to dislodge the infantry from their positions on the hill.

The battle was fought throughout the day, becoming a gruelling stalemate in which neither side won a clear advantage. King Charles, appalled at the bloodshed, rejected his advisors' suggestions that the battle should be continued into a second day and withdrew his forces to Oxford. The two sides had lost about 3,500 men between them but the royalists had come off worst. The Earl of Carnarvon and the Earl of Sunderland had both been killed in the fighting. Most dismayingly of all for the king, Viscount Falkland, his Secretary of State, had effectively committed suicide by riding deliberately to his death in apparent despair at the horror of the civil war.

The second Battle of Newbury would occur a little over a year later.