Gytis Masiulis made his youth debut for Lithuania at the 2014 FIBA Europe Under-16 Championship in Latvia. He won a bronze medal with Lithuania in the 2015 FIBA Europe Under-18 Championship. One year later, he won silver medal at the 2016 FIBA Europe Under-18 Championship in Turkey. In 2017, Masiulis represented Lithuania at the 2017 FIBA Under-19 Basketball World Cup.