João Mário represented Portugal at the UEFA European Under-21 Championship in 2015, netting the only goal of their opening group win over England as the tournament ended with a runner-up finish. He was selected by the full side for their UEFA Euro 2016 campaign, starting in the first match, a 1–1 draw with Iceland in Saint-Étienne; he played in all of his team's seven games during Euro 2016, including the final against France which they won.