In 1928, the newly-established authoritarian regime expropriated the mansion so that it would become the official residence of the President of the Council of Ministers. After the necessary fitting-out works, António de Oliveira Salazar moved to the mansion in May 1938, even though the formal unveiling only took place eleven months later, in April 1939. During the works, a monumental staircase connecting the grounds of the mansion to the Parliament gardens was commissioned to architect Cristino da Silva. When Marcelo Caetano became Prime Minister in 1968, the mansion saw major renovations: little more than the façades were kept. These works also added a new upper floor to the building, where before there was only an old attic.
Post-1974
After the Carnation Revolution on 25 April 1974, the mansion and the gardens were slightly modified, but it was only in 1986, when they saw new renovation works, that the official residence gained greater operability and a modern image. The garage was converted into a building to receive foreign visitors. The old tarmac was replaced with intricately patterned Portuguese pavement. In 2007, in order to increase the residence's energy efficiency, it was equipped with a wind turbine, with a production capacity of 3.5 MWh/year, and photovoltaic panels, capable of producing up to 6.7 MWh/year. Starting 5 June 2016, the gardens of São Bento Mansion are open to the public on Sundays, bar those in which visits would collide with the Prime Minister's official schedule. These visits were a result of a protocol between the Presidency of the Council of Ministers and the Lisbon City Council. Starting on 5 October 2017, the year-long exhibition "Arte em São Bento", also visitable on Sundays, saw the mostly academic art collection in the residence be replaced with works from the SerralvesContemporary Art Museum. The intention is to change the art collections there every year, on 5 October. and Pedro Sánchez, Prime Minister of Spain, in July 2020 Even though it has been the official residence of the Portuguese Prime Minister since 1938, very few Prime Ministers have since opted to actually live there during their respective terms in office. Those who have were António de Oliveira Salazar, Vasco Gonçalves, José Pinheiro de Azevedo, Carlos Mota Pinto, Aníbal Cavaco Silva, and Pedro Santana Lopes. In 2018, it was announced that several reports identified safety issues on São Bento Mansion; from April to October of that year, the gardens were closed and the residence was renovated with new heating, ventilation and air conditioning, electrical wiring and fire protection systems. In the meantime, the Office of the Prime Minister was temporarily moved to the old premises of the Ministry of the Sea, in Commerce Square.
