The centre-back was born in Birmingham but has represented the Republic of Ireland thanks to his grandfather, who was born there. His career started at Peterborough United, where he came through the youth team and broke into the first team in 2002. He played as a centre-back but could also operate at full-back or in midfield. His face was perhaps more common to those who watched the Sky series 'Big Ron Manager', a behind-the-scenes look at Posh's struggle to get into the League Two play-offs in the 2005-06 season.

He made the step-up the league ladder when he signed for Preston North End, signing in 2006 for a fee of £225,000 in July 2006 and went on to make 185 league appearances for the club, netting 10 league goals along the way. It was here where he won the majority of his international caps. He moved to Middlesbrough on loan with a view to a permanent deal in September 2009 but he failed to settle at the club and returned to Lancashire.

With Preston suffering relegation, St Ledger made the switch to City in July 2011, penning a three-year deal for a fee believed to be around the £1.2 million mark. He did, however, make a bad mistake in his debut against Bristol City, something which saw him lose his place for a while.