Simon de Montfort's Parliament was an English parliament held from 20 January 1265 until mid-March of the same year, called by Simon de Montfort, a baronial rebel leader.

Montfort had seized power in England following his victory over Henry III at the Battle of Lewes during the Second Barons' War, but his grip on the country was under threat. To gain more support, he summoned not only the barons and the knights of the shires, as in previous parliaments, but also burgesses from the major towns. They discussed radical reforms and temporarily stabilised Montfort's political situation. Montfort was killed at the Battle of Evesham later that year, but the idea of inviting both knights and burgesses to parliaments became more popular under Henry's son Edward I. By the 14th century, it had become the norm, with the gathering becoming known as the House of Commons.