The parliamentarian army deployed in traditional fashion with cavalry on the flanks and infantry in the centre with a line of artillery pushed out in front of the infantry. Sir Arthur Hesilrige commanded the right wing of parliamentarian horse, Acting Major General James Carr with Colonel Alexander Popham commanded the centre and Sir Edward Hungerford the left wing. The royalists faced them with three brigades of horse. Lord Wilmot’s brigade deployed on the left with Sir John Byron’s brigade to its right. The Earl of Crawford’s brigade was held in reserve.
In an initial skirmish between forlorn hopes some parliamentarian dragoons were routed which appears to have allowed the royalists to destroy most of Waller's gun line before returning to their ranks. Wilmot then met Sir Arthur Hesilrige in a clash of the horse and eventually defeated him, causing his men to flee back through their second line which they carried away. They fled around the rear of the foot and hotly pursued fled west. The parliamentarian horse on the left wing then moved forward, only to be met by Byron's brigade which, after a prolonged struggle, also drove them back into their reserves. An attempt by Parliament's third line to help was nullified by Crawford's brigade and Waller's whole left wing dissolved into confusion and ran with many crashing down precipitous slopes to their deaths. The foot stood alone on the hill.
Surrounded, the infantry tried to march off west, towards Bath, but it became obvious they were in grave danger when Hopton's infantry were seen emerging from Devizes to join the attack. Their commanders fled and although they made a brave attempt to quit the field they were pinned by the cavalry and then probably attacked by the infantry. They broke and ran. A determined rearguard action was fought where the Bath Road began its descent of Beacon Hill, giving a good number the opportunity to get away, but the battle was a humiliating defeat for Waller. He called it 'the most heavy stroke that ever did befall me' whilst the royalists called it 'Runaway Down'.