The two sides were in place by eleven on the morning of 14 June. Prince Rupert began the battle with a charge that pushed back Ireton's cavalry, some of whom fled. Seeing this, the Royalist infantry also advanced, and the Parliamentary centre was forced back. This was the high point of Royalist success. Cromwell, with half of his cavalry, now charged against Langdale, who was himself pushed back. Meanwhile, Rupert, who this time had managed to keep his cavalry on the field, had turned to aid the Royalist cavalry, only to find himself attacked on the flanks by that half of Ireton's cavalry which had not yet engaged. Cromwell now used his remaining, fresh, troops, to drive Langdale's men off the field. That left the Royalist infantry exposed to Cromwell's Ironsides, and under their pressure, the Welsh levies broke, and surrendered in large groups, leaving their officers with no choice but to flee or be captured. The only remaining Royalist forces still fighting were Rupert's Cavalry, who managed to rescue the King, and escape to relative safety in Ashby de la Zouch, some thirty miles from the battlefield. By one in the afternoon, after only two hours of fighting, Parliament had it's victory.
That victory was almost overwhelming. The Parliamentary forces captured the Royalist baggage train, where they captured many of wives of Royalist officers, great amounts of valuables, and perhaps most importantly, the King's entire correspondence. Charles I was left without any infantry, with his guns lost to the victorious Parliament, and with his cavalry scattered. Three days later, the Royalist garrison of Leicester surrendered, and with them Charles lost his remaining arms. In the aftermath of the defeat, many of the remaining Royalist garrisons surrendered. Although Goring's Western army remained intact until the battle of Langport (10 July 1645), Naseby ended any realistic hopes of a Royalist victory. It also raised the profile and prestige of Oliver Cromwell, whose Ironsides had played the most obvious role in Parliament's victory.