The Parliament of Catalonia dates back to the Middle Ages, originating in two institutions: the assemblees de pau i treva (assemblies of peace and truce) and the Cort Comtal (Court of Counts). Initially, the pau de Déu (peace of God) was the right of refuge for people and goods on protected ground within thirty paces of a church, known as sagrera (holy). The treva involved the suspension of war and violent conflict for specified periods.

These “assemblies of peace and truce” promoted by the ecclesiastical establishment were adopted by the sovereign power, the Counts of Barcelona, to halt the continual private wars between feudal lords by establishing a system of guarantees and compensation for the clergy and the civilian population, as well as sealing agreements over taxes. These regulations encouraged the development of towns and markets, stimulating the commercial life of the country.

The first assembly took place in 1027 at Toluges in the County of Rossellon, in the presence of Bishop Oliba of Vic. Few assemblies were called in the following century, and most peace and truce agreements were in fact reached at the court of the Prince (Count of Barcelona, King of Aragon from 1137). In this way the two institutions came together. Many “peace and truce” regulations were included in the Usatges de Barcelona (Barcelona Usages), the earliest Catalan legislative text, enacted by Count Ramon Berenguer I. They were also incorporated into Catalan civil and constitutional law in the late Medieval and modern periods; some even survive in today's civil legislation.

During the 11th century, as the Counts of Barcelona became established as sovereign princes, the Catalan Cort Comtal was constituted as an offshoot of the Frankish Cúria Reial (Royal Court). The Cort consisted of civil and ecclesiastical dignitaries, senior councillors and judges. Their mixed remit helped the sovereign take decisions in legislative and fiscal matters, and assisted him in the exercise of his legal authority.