The Battle of Lewes occurred in the context of the Second Barons' War, which was driven by discontent with King Henry III’s rule and his perceived failure to address the concerns of the barons. The conflict arose due to a combination of political tensions, economic struggles, and the king's favoritism toward foreign influences. Simon de Montfort emerged as a leading figure among the barons, advocating for reforms and greater representation in Parliament. On May 14, 1264, his forces engaged with King Henry's troops outside the town of Lewes in Sussex. The battle resulted in a remarkable victory for de Montfort, who leveraged his strategic acumen to outmaneuver the royal army and secure the king's surrender.

After the battle, King Henry III was captured along with his son, Prince Edward, significantly shifting the power dynamics in England. Following this, the Mise of Lewes was enacted, a document that imposed governance reforms and established a council led by de Montfort. This arrangement allowed de Montfort to exercise a form of quasi-rule over England, as the king was kept from exercising his previous powers autonomously. The barons' victory, however, was short-lived, as internal divisions and subsequent conflicts would lead to further instability and de Montfort’s eventual defeat and death at the Battle of Evesham in 1265, restoring royal authority.