In December 2013, readers of "Waking the Red", a Toronto news site, voted Caldwell the team's best player of the 2013 season. He was given a similar honour by the Red Patch Boys. He was demoted from team captain following the promotion to captain of designated player and American national team mainstay Michael Bradley. He retired in July 2015. Caldwell won twelve caps for Scotland at senior international level. He made his debut in a 1–1 draw away in Poland at the Zdzisław Krzyszkowiak Stadium on 25 April 2001 after breaking into the Newcastle United first team. His home debut came on 12 February 2003 in a 2–0 defeat to the Republic of Ireland at Hampden Park. He played twice in Scotland's qualification for the 2006 World Cup, in a 1–1 draw with Moldova at the Zimbru Stadium in Chişinău and a 3–0 away win over Slovenia at the Arena Petrol in Celje. He took part in Scotland's 2010 World Cup qualification, playing in a 4–0 defeat to Norway as Scotland finished third, behind Norway, in their qualifying group. He briefly captained Scotland when a substitution took place in a 3–0 win against the Faroe Islands on 16 November 2010. His twelfth and final full cap came against Northern Ireland in the 2011 Nations Cup. In February 2019, Caldwell was named president of Oakville Blue Devils FC of League1 Ontario, the third division in the Canadian soccer league system. Caldwell became an assistant coach of the Canada men's national soccer team under John Herdman in September 2019.