Fernandes made his senior debut for Portugal in November 2017, after previously being capped at under-19, under-20 and under-21 levels. He also represented Portugal at the 2016 Summer Olympics. He was chosen in Portugal's squads for the 2018 FIFA World Cup, 2019 UEFA Nations League Finals and UEFA Euro 2020, winning the 2019 competition on home soil while being named in the Team of the Tournament.