Born in Dublin, Dicker began his career at League of Ireland side UCD. He joined from his local junior club Cherry Orchard and was gradually introduced into the first team through substitute appearances towards the latter end of UCD's successful 2004 First Division campaign. Dicker progressed his way into a regular starting position the following season and successfully partnered Tony McDonnell in central midfield for the 2005 and 2006 Premier Division seasons. During his time at UCD he earned underage honours for Ireland at under-19 and under-21 level. In the 2006 League of Irelandclose season he spent a loan spell at Championship side Birmingham City, but he never made it past the reserve team. He made his debut for the Birmingham City reserves against Stoke City Reserves, which Birmingham won 3–0. The Birmingham reserve team coach, Keith Bertschin, described Dicker as a "very decent player. He's a good technical player, who can see and put in some lovely weighted passes and is decent with both feet".
Dicker was signed by manager Jim Gannon for Stockport County on 29 May 2007, for a fee of just £40,000, signing a contract until 1 July 2010. He played a regular part in Stockport's 2007–08 League Two campaign and took part in a promotion for the second time in his career as County successfully negotiated their way into League One via the playoffs. Dicker was a fan favourite during his time at Stockport for his passing ability and off the ballwork rate. Dicker scored his only goal for Stockport in November 2008, opening the scoring in a 5–0 win in an FA Cup first-round tie at home to Yeovil Town.
Brighton & Hove Albion
On 26 March 2009, Dicker joined League One side Brighton & Hove Albionon loan for the remainder of the season. He made nine appearances for the Seagulls, scoring one goal, during this spell. On 25 June, he joined Brighton on a free transfer, signing a two-year contract. On 28 April 2011, having helped Brighton secure promotion to the Championship, Dicker was rewarded with a two-year contract extension. He was released when that contract expired at the end of the 2012–13 season.
On 27 June 2014, Dicker signed a two-year deal with League Two side Carlisle United.
Kilmarnock
On 1 February 2016, Dicker moved to Scottish Premiership club Kilmarnock, signing an eighteen-month contract. He made his debut in a Scottish Cup tie away to Rangers five days later.
