The balance of power in the North changed dramatically in 1644 when the Scottish Covenanter army, allied to and funded by the English Parliament, crossed the border and entered the war. By the spring of 1644 the Earl of Newcastle's Northern royalist army had retreated behind the defences of the city of York. There he was besieged by three allied Parliamentarian forces. These comprised the Northern Association army of Lord Fairfax, the Earl of Manchester's Eastern Association army from East Anglia, and the Scottish Covenanter army under the Earl of Leven; some 28,000 troops in total. Despite intensive bombardment from close quarters and attempts at storming the defences, the city still held out in late June.

Since Roman times York had been the key to the North. If the city fell then the royalist grip on the North, secured following the victory at Adwalton Moor, would be in jepoardy. In response Prince Rupert was despatched by King Charles to raise the siege. Approaching via Lancashire, where he collected reinforcements after successful actions at Stockport, Bolton and Liverpool. Rupert then crossed the Pennines and advanced towards York at the end of June at the head of some 14,000 troops. Fearing his deserved reputation as a formidable commander, unnerved by his rapid advance and fearing Rupert’s force was greater than was actually the case,  the allied generals raised the siege of York on 1st July. With the intention of intercepting Rupert, the allied commanders gathered upon Marston Moor some seven miles west of the city. Rupert was not to be drawn and continued his approach to the relief of York. Marching 20 miles in a day Rupert had entered York by the evening of July 1st.

Emboldened by his success, Rupert was now eager for battle, claiming he had instructions from Charles I to engage and destroy the allied armies. Despite the cautionary words of the Marquis of Newcastle, the commander of the King's northern army based in the garrison at York, who urged restraint, Rupert headed west to Marston Moor on the morning of 2nd July. The Parliamentarians meanwhile, having been outwitted and outmanoeuvred by Rupert on the previous day, had decided to withdraw towards Tadcaster, from which direction reinforcements were expected. Sir Thomas Fairfax (the son of Lord Fairfax) was in the rearguard of the parliamentary force. Seeing Rupert’s vanguard of cavalry approaching he alerted the Earl of Leven who, having almost reached Tadcaster, at once returned with the rest of the army to Marston Moor.