Delaney began his career at Cork City. He later played for Leicester City, Hull City and Queens Park Rangers before moving to Ipswich Town in 2009. He became a free agent after leaving the club in August 2012. He then signed for Crystal Palace as he became a vital player in the centre of defence in their promotion season.
Born in Cork, Delaney attended Coláiste Chríost Rí and began his career at local club Avondale United at schoolboy level before moving on to Cork City.
He also played football with the Cork minor team. Delaney was a Munster minor football winner with the team in 1999 and shone for his club St Michael’s. He struck 2–2 in an All-Ireland semi-final defeat to Mayo that year, before he committed fully to soccer. He has explained he never demanded a guaranteed starting berth with his country
He was brought to England by Peter Taylor at Leicester City, where he made eight FA Premier League appearances. He had spells on loan at Stockport County, Huddersfield Town and Mansfield Town. Whilst at Stockport, he scored his first career goal in a match against Rotherham United. Taylor later made Delaney his first signing for Hull City, on 16 October 2002, for a fee of £50,000.
After a rocky start to his career at Hull, during which time he was tried in midfield and at left-back, Delaney was played regularly at centre-back and began to grow in stature and consistency. He was voted Player of the Year in the 2003–04 promotion-winning season, additionally his strike against Rochdale was voted Goal of the Season.
In the 2005–06 season in the Championship, he played mainly at centre-back, but also at left-back when two players in that position were injured, and in midfield when the manager felt that more height and solidity were required. This versatility made him a key asset to the Tigers squad.
Delaney was the last Hull City player to score a goal at their old ground Boothferry Park, prior to their move to the KC Stadium.
On 18 January 2008 Delaney signed for Queens Park Rangers on a three-and-a-half-year contract. On 8 March 2008 Delaney scored his first goal for QPR in a 2–1 away defeat to Sheffield Wednesday.
On 2 July 2009, Delaney signed for Ipswich Town on a two-year contract for a fee of £750,000, £250,000 if Ipswich reached the play-offs and an extra £100,000 after he has made 50 appearances for the club. He suffered a freak injury in the following year's pre-season which almost cost him his life. A blood clot in his thigh resulted in him potentially losing a leg but he was rushed to an emergency surgery procedure that resolved the issue. He scored his first goal for the club in the East Anglian derby in November 2010, before being sent off following a straight red card. He left the club by mutual consent in August 2012.
On 31 August 2012, following his departure from Ipswich, Delaney signed for Crystal Palace on a short-term contract until January 2013. He scored his first goal for the club in Palace's 4–3 comeback against Burnley on 6 October. Due to Delaney's impressive start to his Palace career, he signed a new contract on 22 November 2012, which expires summer 2014. He scored his first ever goal in the Premier League in a 3–3 draw against Liverpool, with his initial 25-yard shot deflected slightly into the net by Glen Johnson. Palace were 3–0 down at the time, but Delaney's goal combined with two goals from Dwight Gayle made it 3–3.
On 13 May 2008, Delaney was called up to the Republic of Ireland squad for the first time by the new manager Giovanni Trapattoni. On 4 May 2011, he was called into the Irish squad for the 2011 Nations Cup games against Northern Ireland and Scotland. On 24 May 2011, he started and played the full 90 minutes against Northern Ireland as Ireland beat them 5–0. On 11 October 2013, he made a belated competitive debut in a World Cup qualifier against Germany.As of match played 19 September 2017
Cork CityLeague of Ireland Cup: 1998–99
Hull CityFootball League Third Division runner-up: 2003–04
Football League One runner-up: 2004–05
Crystal PalaceFootball League Championship play-offs: 2013
Republic of Ireland
Nations Cup: 2011