In the early hours of the morning of Sunday 18th June 1643 Rupert surprised parliamentarian quarters at Postcombe and Chinnor destroying a troop of horse and killing or capturing 170 dragoons. He then continued on in the hopes of surprising a pay convoy, though leaving Chinnor in flames behind him was perhaps not the most appropriate means of maintaining surprise. With the alarm raised Rupert acknowledged the attempt as abortive and headed back to Oxford. By now the parliamentarians were pursuing as he headed for the bridge over the river Thame at Chislehampton. With the parliamentarians closing on him, Rupert chose to turn and fight. He dispersed the dragoons along the lane leading to the bridge, so protecting his line of retreat, sending the infantry on to secure the bridge. He then deployed his 1,100 strong cavalry in the open fields of Chalgrove.
 
The parliamentarians descended westward from Golder Hill on one side of a 'great hedge' which formed the parish boundary, following Rupert on the other side of that hedge.  At the bottom of the large enclosure in which they found themselves, the parliamentarians deployed by some trees.  Rupert then rode away, enticing his opponents to follow, which they did, presumably using the gap in the 'great hedge'  formed by what is now Warpsgrove Lane. 

Either at Upper Marsh Lane or further to the west, Rupert turned and faced  the parliamentarians behind another smaller hedge. Despite being outnumbered, having only around 500 horse, the parliamentarians advanced their dragoons and fired upon the Royalist troops from the cover of the hedge. Parliamentarian propaganda describes their action as gallant, but in reality one would expect dragoons to be deployed forward on foot to line the hedge, firing from its cover to hold it against cavalry.
 
In characteristic style, Rupert led the attack, he and some of his cavalry jumping the hedge that separated the two forces, causing the parliamentarian dragoons to break and flee, though not without inflicting casualties. The remaining parliamentarian troops engaged the royalist cavalry first with carbines and pistols at range and then in melee before they too broke and ran. Although the Royalist accounts credit the parliamentarians with standing ‘our first charg of Pistols and Swords, better than the Rebells have ever yet done, since their first beating at Worcester’ the action was short and rapidly became a rout with the parliamentarians fleeing back to their reserves, who were unable to hold the royalists and the action became a rout. In the confusion Hampden, fighting as a volunteer, was shot twice in the shoulder. He was able to ride back to Thame but six days later, on 24th June, he died of his wounds.
 
Following the victory Rupert continued his retreat to Oxford. Although he had failed in his initial intent to capture the parliamentarian payroll he had very effectively demonstrated the ease with which his troops could out-manoeuvre Essex.