Whilst at Stamford Bridge he often found himself as back-up to the likes of Dmitri Kharine and Frode Grodas and spent time on loan at Crewe Alexandra, Grimsby Town, Millwall, Brentford and Reading.

In 2004 following a loan spell with Stockport County he joined Barnsley where he played for four years and also helping the club to promotion to the Football League Championship in 2006.

The Blues were managed at the time by Ian Porterfield and Colgan was designated as the third choice keeper at Stamford Bridge behind Dmitri Kharine and Kevin Hitchcock.

In September 1993, Colgan was signed by Dario Gradi in a one-month loan spell with Crewe Alexandra, however he failed to make an appearance for the club and soon returned to Stamford Bridge.

During the 1994–1995 season joined up with Alan Buckley at Grimsby Town who used him as a deputy keeper to Paul Crichton, but also Colgan went unused at Blundell Park during his spell in Humberside.

The Chelsea team that day featured the likes of Gianfranco Zola, Gianluca Vialli, Dan Petrescu, Dennis Wise and Mark Hughes.

His first season at Easter Road he made 31 appearances for the club, and was looked upon as the first choice keeper in a side that boasted Olafur Gottskalksson and John Campbell.

County were under a squad re-shuffle that had seen them use Lee Jones, James Spencer, Boaz Myhill, Anthony Williams and Colgan in the net that season.

His outstanding displays during the season earned him 20 clean sheets in total as well as the title of Barnsley's Player of the Year and helped the team reach the League One Play-off final at the Millennium Stadium in Cardiff on 27 May 2006 where despite a mistake letting Swansea City take the lead, he recovered to make a historic save from Alan Tate in the penalty shoot out which ensured Barnsley won their place back in the Championship.

He failed to make an appearance for Town, after fellow keeper Stephen Bywater was loaned in from Derby County who kept the goalkeeping shirt for the remainder of the season.

[7] He was eventually released on 28 May 2009 by Keane's replacement Ricky Sbragia along with six other first team players, notably Dwight Yorke, Rade Prica and David Connolly.

Over the Easter weekend period, injuries to both Colgan and his young understudy Overton meant that Mark Oxley was signed on an emergency loan to deputise.

It was also stated that the signing of Rochdale's Kenny Arthur as Grimsby's new first choice keeper could sway Colgan's decision into leaving the club in favour of remaining as Town's back up goalkeeper for the upcoming season.

On 15 October 2010, Colgan moved on a month's loan to Football League One side Huddersfield Town, as cover for the injured Alex Smithies and the experienced Ian Bennett.

[13] On 21 January 2011, Colgan re-signed for Huddersfield Town on a contract running to the end of the season, mainly as back-up for Ian Bennett, while Alex Smithies is recovering from injury.

He went on to make a total of ten appearances for his country,[2] but was selected many more times for the national squad as a backup to the likes of Shay Given and Paddy Kenny.