[9] Kilgallon was first called up to the first team for a UEFA Cup match away to Metalurh Zaporizhya on 3 October 2002,[10] although he did not make the matchday squad.

[citation needed] He played in their run to the 2006 Championship play-offs, helping them make the final, which Leeds lost 3–0 against Watford at the Millennium Stadium.

[13] He played in most of Leeds's matches of the first half of the 2006–07 season, keeping experienced centre-backs Paul Butler, Sean Gregan and Hayden Foxe out of the team.

[16] He scored his first goal for Sheffield United on 15 December 2007, with a deflected header in the 64th minute of a 1–0 home victory over local rivals Barnsley.

[19] At the turn of the year, Kilgallon announced that he intended to see out the remainder of his contract[20] and rejected the opportunity to open transfer talk with Premier League club Burnley.

[23] Kilgallon struggled to make an impact during Sunderland's winless run until a man-of-the-match performance against Hull City on 24 April 2010, his first start in months.

[citation needed] On 1 January 2012, Kilgallon made his first Sunderland appearance since May 2010, coming on as a 26th-minute substitute for the injured Wes Brown against Manchester City.

[28] Two days later, he made his first Sunderland start since May 2010, playing alongside John O'Shea in central defence in a 4–1 away win against Wigan Athletic.

[29][30] He suffered an ankle injury during a 1–0 away defeat against Chelsea on 15 January 2012[31][32] and did not reappear until 31 March, starting in an away match against Manchester City.

[34] After playing in Sunderland's 3–0 loss away to Liverpool on 2 January 2013, he did not feature again in the league under Martin O'Neill, but returned to the starting line up for Paolo Di Canio's first match in charge, a 2–1 defeat away to Chelsea, in which scored an own goal.