Carson was first called up to the England under-21 squad in October 2003, a month after his 18th birthday, for the 2004 UEFA European Under-21 Championship qualifier against Turkey. At the time he was yet to make his competitive debut for Leeds United's first team, and had previously played only four matches for England at other levels. He made his under-21 debut in a 3–2 win for England against the Netherlands in February 2004. He was selected in the squad for the 2007 UEFA European Under-21 Championship, and in the third match against Serbia, he earned his 28th under-21 cap, eclipsing the record held by Gareth Barry and Jamie Carragher. His 29th and final cap came against the hosts, the Netherlands, in the semi-final, which finished level at 1–1 after extra-time. In the resultant penalty shoot-out, he saved one of the 16 penalties he faced and also scored one himself, but England lost 13–12. Carson has since been overtaken by James Milner as the England Under-21 team's most-capped player.