Johnston was nine years old when he was first spotted by Liverpool and he signed his first professional contact in May 2017. Last season Johnston represented the club in the Under 23 Premier League 2 competition, making 36 appearances and scoring four goals. The Scotland youth international also found time to make his first-team debut in a friendly at Anfield against Torino.
Technical director Sjaak Troost said: ‘George is a talented defender who can play in various positions at the back. There was interest from the Premier League and elsewhere, but he chose Feyenoord with the aim of developing under Jaap Stam into an important player at De Kuip.’