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 Ireland close 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'.
He officially signed for Stockport County on 29 May 2007, by manager Jim Gannon 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 ball work rate. Dicker scored his first and only goal for stockport in a F.A Cup first round tie at home against Yeovil Town F.C. dicker scored the first of five in a 5-0 win.
On 26 March 2009, Dicker initially joined League One side Brighton & Hove Albion on loan for the remainder of the season, where he made nine appearances for the Seagulls, scoring one goal during this spell. On 25 June 2009, Dicker, 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.
Dicker, alongside Vicente and Marcos Painter were released at the expiration of their contracts on 16 May 2013.
On 13 September 2013, Dicker joined Rochdale on an initial five-month deal.
On 23 January 2014, Dicker joined Crawley Town for the remainder of the 2013–14 season.
On 27 June 2014, Dicker signed a two-year deal with League Two side Carlisle United.
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 on 6 February 2016.
Stockport CountyLeague Two play-offs: 2008
Brighton & Hove AlbionLeague One: 2010–11