Bloc de gauche
In November 2015, Matias announced her candidacy for the 2016 Portuguese presidential elections, representing the Left Bloc party. She finished 3rd, with 10,12% of the votes, the best result ever achieved by a woman in a presidential election in Portugal at the time. She was also a candidate for Left Bloc in the 2021 Portuguese presidential election in which she came 5th, with 3.95% of the vote.