The city of Montemor-o-Novo – seat of the municipality - is an ancient settlement, originally located on the inside of the fortified walls of the castle, expanding later throughout the hill facing north, where it stands at present.
The municipality received charters from Kings D. Sancho I (1203)and D. Manuel (1503) and played an important role in the fight against the Castilian occupation (1580 - 1640) and during the French invasions (at the beginning of the 19th century).

The golden era for the city of Montemor-o-Novo occurred during the 15th and the 16th centuries, when the prosperity brought by trade was allied to the fact that the court spent long periods in Évora, making Montemor-o-Novo a place where relevant political events took place, as well as being a meeting place for the court when the King took up residence in Paço dos Alcaides.
It was in Montemor, in the year 1496, that King D. Manuel I took the historical decision to order the discovery of the maritime route to India, during the general councils that took place in the city.

In the survey commissioned in 1527 by King D. João III, the first census of the population carried out in Portugal, Montemor is listed as having 899 houses, holding the sixth place among the lands of Alentejo. In 1563, King D. Sebastião granted Montemor the title of “Notable City”, as it was "an ancient locality with a large population" surrounded and enriched by churches, temples, monasteries and many other buildings and noble houses".
Some of the more important works of architecture in the city date from that period, such as the buildings of the Misericórdia, the convents known as Convento da Saudação, Convento de São Francisco and Convento de Santo António, the chapel of Nª Srª da Visitação, the old hospital known as Hospital Velho and the main entrance door of the church of Santa Maria do Bispo.
As for historical events some are worth mentioning as exceptional in the quiet life of the local population:  the resistance to the first invasion by the French, led by Junot, in 1808, near the Lisbon bridge; the stationing, in 1834, of the liberal army headquarters  led by Saldanha, during the civilian fights between the liberals and the “miguelistas” (those in favour of D. Miguel I of Portugal); the visit of Queen D. Maria II and King D. Fernando II in 1843.

Montemor-o-Novo played a very active role in the resistance to the fascist dictatorship and in the struggle for a better way of life for the people and for freedom.    

During the Portuguese revolution on the 25th of April 1974, Montemor-o-Novo stood at the forefront of events that led to remarkable achievements such as the implantation of Local Democratic Power and the Agrarian Reform.

Montemor-o-Novo was classified as a city by decision of the Assembly of the Republic on the 11th of March 1988 and this is another important date in the recent history of this city.