Newcastle United Caldwell started his career with
Celtic Boys Club. At 16 he went to England, alongside his elder brother Steven at
Newcastle United. Breaking through from the reserves proved difficult, however, and in search of first team football, he went on loan to other clubs on several occasions:
Darlington and
Hibernian in 2001–02, He signed a short-term contract with Hibs for the second half of the season, This prompted Hibs fans to
jeer Caldwell when he made a mistake in a game against
Aberdeen. Caldwell himself later said that this was due to injuries in his first season, and then having to play out of position at right back during the early part of the 2007–08 season (before
Andreas Hinkel was signed). Caldwell apologised to Fernandez after the game, protesting that he had never intentionally hurt an opponent. After being named as the
Writers' Player of the Year for the
2008–09 season, Caldwell stated his belief that this was due to him having a long run in his preferred position, and improved concentration and decision making on his part. New manager
Tony Mowbray, who had also worked with Caldwell at Hibernian, responded by stating that he would not ask the board to increase the offer.
Wigan Athletic Caldwell eventually signed for
Wigan Athletic on a four-and-a-half-year contract for an undisclosed fee on 13 January 2010. He made his Wigan debut in a 2–0 win against
Wolves on 16 January 2010, and scored his first goal for Wigan in a 2–1 defeat to Blackburn Rovers on 27 January. Caldwell was sent off twice in Premier League defeats against Manchester City on 29 March (3–0) and
Chelsea on the final day of the 2009–10 season (8–0). Caldwell was appointed captain of Wigan Athletic early in the 2010–11 season, following the departure of previous captain
Mario Melchiot in the summer. In the 2011–12 season, Caldwell was a key player in the club's battle against relegation from the Premier League, and received the club's Player of the Year award at the end of the season. In May 2013 he jointly lifted the FA Cup with playing captain
Emerson Boyce after Wigan defeated Manchester City 1–0 in the
final. Caldwell returned from injury as a substitute in the
2013–14 FA Cup semi final against
Arsenal. The match ended in a 1–1 draw, but Caldwell missed the first attempt in the penalty shootout, which Wigan lost. In the
2013–14 Football League Championship playoff semi final second leg against QPR, Caldwell conceded a
penalty kick during a 2–1 defeat that ended Wigan's hopes of promotion. Caldwell signed a one-year contract with Wigan in July 2014. As part of the new agreement he was also given some coaching responsibilities. He announced his
retirement from playing on 28 February 2015 after being unable to recover from a long term hip injury. ==International career==