[2] On 7 October 2018, while still a junior, he made his professional debut with the reserve team in a LigaPro match against F.C.
[4] On 10 June 2020, João Mário had his first call-up to Porto's first team, remaining unused as they won 1–0 at home to C.S.
[5] He debuted on 15 July as they won the Primeira Liga title with a 2–0 win over Sporting CP also at the Estádio do Dragão, playing the last five minutes in place of Luis Díaz.
[9][10] João Mário won his first cap for Portugal at under-21 level on 4 September 2020, and scored in the 4–0 away victory against Cyprus for the 2021 UEFA European Championship qualifiers.
[11] On 13 November 2023, João Mário was called up by the senior team for the first time, replacing Diogo Dalot (who withdrew for personal reasons) in the squad that would face Liechtenstein and Iceland in UEFA Euro 2024 qualifying matches.