In May 2010, Gylfi made his full Iceland debut in a convincing 4–0 win over Andorra and provided the assist for the second goal from a free-kick. Gylfi also helped Iceland's U21 side reach the 2011 UEFA European Under-21 Championship, playing in both play-off legs against Scotland as Iceland won 4–2 on aggregate. In the second leg, Gylfi scored two second-half goals to ensure Iceland won the match 2–1.