Daniel Agger played for the various Denmark youth teams before making his debut for the senior team in 2005. The defender featured for the u-20 team and the u-21 team before playing his first game for the senior team.
Agger scored once in ten games for the Denmark u-20 teambetween 2003 and 2004. He also scored three times in ten matches for the Denmark u-21 team between 2004 and 2006. His senior team debut came in a friendly match against Finland on June 2, 2005. The centre back played the whole game which ended in a 1-0 victory for the Danes. He was then benched for the next senior national team game. His second cap came against England on August 17, 2005. Daniel Agger partnered Per Nielsen at the heart of the Danish defenceduring a friendly game which ended in a 4-1 win for his team.