The English Civil war had been raging for some two and a half years before the Royalists and the Parliamentarian armies met at a point located in the heart of the country. This was to be a battle which would go a very long way to sealing the fate of the whole war.

The Royalists or Cavaliers had been steadily losing ground in their fight against Cromwell and his Roundheads. The Royalists had recently taken the city of Leicester from parliament, after which a massacre ensued, but this was for them a brief flicker of light in the darkness. The New Model Army that had been created by Parliament had been besieging the city of Oxford while King Charles and his chief advisors were camped at Daventry in Northamptonshire discussing their next move. The Scots to the north were one possible target for the Royalist army while a consolidation of power in the southern counties in order to face the Roundheads more convincingly was also an option.

The Roundheads were of superior numbers and, it is well reported, superior leadership. King Charles was indecisive which was in sharp contrast to the commander of the Roundhead forces, Thomas Fairfax. Fairfax was a very good commander and with the appointment of Cromwell as his second-in-command the New Model Army could now be seen to fully on the offensive. With their bloody victory at Leicester in mind the Royalist army was high in spirits while the arrival of Oliver Cromwell was enough to increase Roundhead morale.

Naseby became the battlefield through the King withdrawing his forces following an advance by Fairfax towards the Daventry encampment. The King marched north towards Market Harborough. It was at Naseby that his advance units were discovered by the Roundheads. Further withdrawal was unfeasible thus the battle was forced.

The Royalists had scant knowledge of the Roundhead positions, the scouts they had sent forward either being captured or returning with false information. At the outset of the battle the Royalists believed that the enemy was in retreat.

Prince Rupert, general in the Royalist army, took no trust in the words of the scouts and went forward to look for himself. He discovered a Roundhead cavalry unit retiring ahead of him. He then believed that the enemy were indeed retreating. Rupert changed his mind about withdrawing away from a stronger enemy force and decided to attack what he thought was the fleeing enemy.

The Royalist advance was steady and regimented, the cavalry in time with the obviously slower foot soldiers. The Roundheads came into sight, their numbers strangely fewer than expected. The Royalists took these men to be the rearguard and the advance continued. It was not until the two sides were within musket range of each other that the full numbers of the Parliamentarian force was seen by the Royalists.

The Royalist advance now seemed folly with a much smaller army attacking a well-drilled larger one face on. The opposing forces lined up in traditional fashion with the main body of infantry, ostensibly pikemen to the fore and musketeers to the rear, in the centre with cavalry on each flank. The Roundheads also had dragoons, mounted troopers with both pistol and sword, and these were positioned to the left flank of the force behind some hedgerows and facing the battlefield from the side.

Prince Rupert, to whom the name 'cavalier' fitted well, charged at the head of his cavalry into Ireton's cavalry. The success of this attack, with the Dragoons firing upon Rupert's flank as they charged, was lost as the reckless prince charged after the majority of Ireton's horse who were now retreating.

Thus part of the Roundhead army had been chased from the field by the best part of the Royalist cavalry, this proved an inequitable trade.

Ireton and several other troopers of his cavalry who had stood up to the charge of Rupert were now able to attack the Royalist foot without hindrance from their cavalry.

The other flank told a different story. It was the Roundheads, led by Oliver Cromwell, who charged first. Despite a valiant defence on behalf of the Royalist cavalry they were either killed or pushed back to find support from the reserves.

The action in the centre began as solely a foot battle. The Royalists had marched on with a regimented step. A volley of musket fire blasted out from the waiting Parliamentarian ranks, followed by the defenders charging at the advancing column. The Royalists fired but one volley before they were engaged in the 'pike and push' skirmish of which this era is famed. Using sword and the stocks of their muskets the Royalists managed to push their enemies back until Fairfax led his reserves into the fight. Ireton's cavalry and Okey's dragoons charged into the flank of the Royalists foot. The fight was not as one-sided as one may imagine and the New Model Army was only saved from defeat with the intervention of Cromwell's horse.

Cromwell's disciplined troopers, having driven Langdale's cavalry off the field, now attacked the Royalist infantry from the rear. Panic swept through the Royalist ranks with a collapse inevitable. The King witnessed the scene and gave orders for Langdale's horse (the remnants of them) to intervene. This order was not followed upon as the intervention, which the King made a show of wishing to lead himself, would have been futile at best and suicidal at worst.

The day went to the Parliamentarians. The discipline of Cromwell's troopers was in sharp contrast to that of Prince Rupert's and combined with the sheer weight of numbers had been decisive in the battle.