The Acclamation Cortes of Mafra was an assembly of all the members of the Portuguese Cortes (composed by the Chamber of Deputies and the Chamber of Lord Deputies of the Portuguese Nation) and the members of the current government of the Kingdom of Portugal, invoked by Prince Hadrian of Portugal, with the intent of being recognized and acclaimed as the King of Portugal. He swore to uphold and defend the constituiton of the Kingdom of Portugal, and was acclaimed as king. A hymn was then sung, to honour the ascension of the new monarch to the throne.

This special session of the Portuguese Cortes took place on the Basilica of Mafra, located inside the Palace of Mafra.