Jason Demetriou whose grandfather is from Cyprus came through the youth ranks at Leyton Orient and signed his first full professional contract with the team in July 2006. He made his league debut in November 2006 when he came off the bench in a 0–0 draw with fellow League One side Yeovil Town. He went on to make 24 appearances in his first year, in both league and cup competitions, mostly as a substitute.
The 2007–08 season was a breakthrough season winning the young talent award for Leyton Orient. Demetriou himself has given much credit to ex-manager Martin Ling for giving him the chance to prove himself at this level of football particularly in the 07/08 season.[
Despite Leyton Orient struggling throughout the 2008–09 season, Demetriou’s performance impressed the fans and was awarded the fans player of the year.
Demetriou then decided to take a chance in Cyprus and signed for AEK Larnaca on 2 June 2010, for undisclosed fee to be able to progress as an international for Cyprus. He said he was very sad to leave Leyton Orient but had to progress in order to play international football.
He went onto to make full International appearances with Cyprus and signed recently for Anorthosis.
