As Portugal is a semi-presidential parliamentary republic, the prime minister is the country's leading political figure and de facto chief executive.

The prime minister is appointed by the president following legislative elections, after having heard the parties represented in the parliament.

Since the Middle Ages, some officers of the Portuguese Crown gained precedence over the others, serving as a kind of prime ministers.

Over time, the role of principal officer of the Crown fell upon the chanceler-mor (chancellor), the mordomo-mor (mayor of the palace) and the escrivão da puridade (king's private secretary).

Although it is the official residence of the prime minister, not all incumbents have lived in the mansion during their term in office.