The English Parliament, in today’s sense, met for the first time in history on January 20, 1265. Namely, the previous gatherings consisted mostly of aristocrats, and participants were not elected as MPs. On the contrary, elected representatives of cities and districts also sat in the parliament which began its work that day.
The Parliament in question was convened by Count Simon de Montfort against the will of King Henry III. Namely, de Montfort led a rebellion against the king during the Second Baron War (1263 – 1264), after which he became the de facto ruler of England.
Parliament met very close to where it meets today – in Westminster by the River Thames. Because of the importance of that first real English Parliament, Simon de Montfort is considered the originator of modern parliamentary democracy. It should be noted that he also convened the Oxford Parliament in 1258, at which time the king was greatly restricted powers.
By the way, Simon de Montfort was actually French by birth. He was born in a French town called Montfort-l’Amaury, about twenty kilometers from Paris. Although a Frenchman, he inherited the countess of Leicester, England, and became influential in that kingdom. Simon de Montfort was killed in August 1265 by the King’s forces at the Battle of Evesham.