De Souza, who has an approval rating of over 60 percent, is widely expected to secure a victory in the election.
The incumbent leader is up against six other candidates, including Andre Ventura from the right-wing Chega party, who is supported by more than 10 percent of the population according to opinion polls. If none of the candidates secure over 50 percent of the vote during the Sunday election, a runoff will take place on February 14.
In Portugal, the president is the head of state and mostly has just ceremonial powers.
COVID-19 restrictions are in place in Portugal and there were no large-scale public events or gatherings during the electoral campaign.