Koroma trained with English side
Watford in October 2007. He impressed, but was unable to secure a contract due to work permit issues. He also trained with
Southampton but again, could not sign a professional contract with the club. In July 2008 he was then offered a two-week trial with
Premier League side
Portsmouth, featuring in some of their pre-season friendlies and impressing enough to be offered a contract. He was eligible for a work permit after recently marrying a British partner. On 4 August 2008 Portsmouth manager
Harry Redknapp confirmed that a two-year contract for Koroma had been completed from
Banjul Hawks, and confirmed that the striker would be spending the
2008–09 season at then
Championship side
Norwich City on loan. He returned to Portsmouth at the end of January but was released the following summer. He trialed in Denmark, trialing for
Brondby IF. He impressed Brondby and
Denmark striker
Peter Madsen when on trial with the
Danish Superliga club. He then went on trial with
Conference Premier side
Forest Green Rovers. He scored a brace in a 2–1 reserve team victory over
Crawley Town on 23 April 2012. After a lengthy trial period with Forest Green, Koroma agreed to a three-year contract at the club in May 2012. He made his Forest Green debut on 27 August 2012 although was sent off after 34 minutes in an away game against
Kidderminster Harriers. After making 20 league appearances for the club, he left on 23 January 2014 by mutual consent. Following a brief trial, he joined
Dulwich Hamlet of the
Isthmian League Premier Division in November 2014, making his debut against
Maidstone United on 12 November 2014, before going on to score his first goal for the club in a 3–1 away win at
Harrow Borough on 22 November 2014. After leaving
Dulwich Hamlet, he moved to
Iceland to sign for
Thróttur Reykjavík on a one-year contract with an option to extend. On 1 March 2016, he signed a one-year contract with
FC Kyzyl-Zhar SK after impressing in their test matches. At the start of the 2016–17 season Koroma joined
Wealdstone of the
National League South, scoring on his debut in a 2-1 league victory over
Margate on 13 August 2016. On 24 March 2017, Koroma re-joined
Dulwich Hamlet on loan for the remainder of the 2016-17
Isthmian League Premier season, with the signing being funded by the club's 12th Man Scheme. Following his release by Wealdstone Koroma rejoined Dulwich Hamlet during the 2017–18 season, spending a spell on loan at
Carshalton Athletic during which he scored five goals in three games,{{Cite web before returning to the Hamlet and making his third debut for the club, starting in a 1–3 loss away to
Enfield Town in the
Isthmian League Premier Division on 3 December 2017.{{Cite web ==International==