Having played with Trojans in the Derry and District League as a youth, Kelly progressed through the Derry City youth system and made his first team debut at home to Sligo Rovers on 18 February 1996.

Newspaper reports in October 2001 claimed Kelly had joined Third Division side Carlisle United, which were denied by Derry, who had rejected Carlisle's £100,000 bid for him.
He featured for Derry in the League of Ireland Cup Final in April 2002, and scored in the penalty shoot-out, which the team lost 3–2.
He eventually became one of many League of Ireland players who joined Carlisle under the management of Roddy Collins in August 2002 for a fee believed to be around £100,000.
He made his Carlisle debut in a 2–0 defeat to Darlington on 27 August.
He featured for Carlisle in the 2003 Football League Trophy Final on 6 April 2003, which they lost 2–0 to Bristol City.
His first goal for Carlisle came as the equaliser in a 1–1 draw against York City and he finished the 2002–03 season with 42 appearances.
Derry revealed they were interested in re-signing Kelly in December 2003, after he was transfer-listed by Carlisle.
Following the end of the 2003–04 season, Carlisle manager Paul Simpson told Kelly he needed to get fit if he wanted to stay at the club.

He was one of three players released by Carlisle, after which he signed a two-year contract for Portadown in August 2004.
Kelly won the 2004–05 Irish Cup with Portadown, and scored in the 5–1 win over Larne in the final.
He became Portadown captain for the 2005–06 season and by December 2005 was being linked with a move away from the club, with his contract expiring in the summer.
He won the Harp player of the month award for February 2006.
He launched a stinging attack on the "prima donnas" at the club and felt some of his teammates lacked "ambition and determination".

Kelly looked set to join League Two side Stockport County on a two-year contract in April 2006, but a day later he said he was yet to decide whether to join them.
Having made 52 league appearances for Portadown he rejected a new contract at the club with the aim of returning to professional football.
He eventually chose to return to his old club Derry City for the second time in May. He played in all of Derry's six matches in the 2006–07 UEFA Cup campaign, which included a goal in the 5–1 victory over Gretna.
He was chosen as the Soccer Writer's Association of Ireland Player of the Month in September 2006.
He was named in the Professional Footballer Association of Ireland's team of the year in December 2006.
He featured for Derry in the first qualifying round of the UEFA Champions League in the 2007–08 season, playing in the 2–0 defeat to FC Pyunik.
He made 29 league appearances in his second spell as a Derry player.

Kelly trialled at Kilmarnock of the Scottish Premier League in July 2007, while Gretna were also interested in signing him, but refused to pay the £50,000 Derry wanted for him.
Inverness Caledonian Thistle and Dundee United had also made inquiries about signing Kelly, although Inverness were only interested in loan terms.
Kelly instead signed for Conference Premier side York City on a two-year contract on 29 August for an undisclosed five-figure fee, with family reasons being his motivation for moving to a British club.
A day after signing for the club, he made his debut against Rushden & Diamonds and scored a late own goal, meaning his new side lost 3–2.
He was ruled out for at least a month with a suspected torn hamstring in January 2008, which was picked up in training, and returned to the side in their 2–0 defeat against Cambridge United on 1 March 2008, after coming on as a 53rd-minute substitute for Darren Craddock.
He finished the 2007–08 season with 33 appearances and two goals for York.
Kelly drew praise from York manager Colin Walker following York's 2–0 victory against Woking in October, which was his first start of the 2008–09 season.
Following this, he admitted fears over his future at York after struggling to feature in the team, having only made two starts since April.
It was confirmed in
Having played with Trojans in the Derry and District League as a youth, Kelly progressed through the Derry City youth system and made his first team debut at home to Sligo Rovers on 18 February 1996.
Newspaper reports in October 2001 claimed Kelly had joined Third Division side Carlisle United, which were denied by Derry, who had rejected Carlisle's £100,000 bid for him. He featured for Derry in the League of Ireland Cup Final in April 2002, and scored in the penalty shoot-out, which the team lost 3–2. He eventually became one of many League of Ireland players who joined Carlisle under the management of Roddy Collins in August 2002 for a fee believed to be around £100,000. He made his Carlisle debut in a 2–0 defeat to Darlington on 27 August. He featured for Carlisle in the 2003 Football League Trophy Final on 6 April 2003, which they lost 2–0 to Bristol City. His first goal for Carlisle came as the equaliser in a 1–1 draw against York City and he finished the 2002–03 season with 42 appearances. Derry revealed they were interested in re-signing Kelly in December 2003, after he was transfer-listed by Carlisle. Following the end of the 2003–04 season, Carlisle manager Paul Simpson told Kelly he needed to get fit if he wanted to stay at the club.
He was one of three players released by Carlisle, after which he signed a two-year contract for Portadown in August 2004. Kelly won the 2004–05 Irish Cup with Portadown, and scored in the 5–1 win over Larne in the final. He became Portadown captain for the 2005–06 season and by December 2005 was being linked with a move away from the club, with his contract expiring in the summer. He won the Harp player of the month award for February 2006. He launched a stinging attack on the "prima donnas" at the club and felt some of his teammates lacked "ambition and determination".
Kelly looked set to join League Two side Stockport County on a two-year contract in April 2006, but a day later he said he was yet to decide whether to join them. Having made 52 league appearances for Portadown he rejected a new contract at the club with the aim of returning to professional football. He eventually chose to return to his old club Derry City for the second time in May. He played in all of Derry's six matches in the 2006–07 UEFA Cup campaign, which included a goal in the 5–1 victory over Gretna. He was chosen as the Soccer Writer's Association of Ireland Player of the Month in September 2006. He was named in the Professional Footballer Association of Ireland's team of the year in December 2006. He featured for Derry in the first qualifying round of the UEFA Champions League in the 2007–08 season, playing in the 2–0 defeat to FC Pyunik. He made 29 league appearances in his second spell as a Derry player.
Kelly trialled at Kilmarnock of the Scottish Premier League in July 2007, while Gretna were also interested in signing him, but refused to pay the £50,000 Derry wanted for him. Inverness Caledonian Thistle and Dundee United had also made inquiries about signing Kelly, although Inverness were only interested in loan terms. Kelly instead signed for Conference Premier side York City on a two-year contract on 29 August for an undisclosed five-figure fee, with family reasons being his motivation for moving to a British club. A day after signing for the club, he made his debut against Rushden & Diamonds and scored a late own goal, meaning his new side lost 3–2. He was ruled out for at least a month with a suspected torn hamstring in January 2008, which was picked up in training, and returned to the side in their 2–0 defeat against Cambridge United on 1 March 2008, after coming on as a 53rd-minute substitute for Darren Craddock. He finished the 2007–08 season with 33 appearances and two goals for York. Kelly drew praise from York manager Colin Walker following York's 2–0 victory against Woking in October, which was his first start of the 2008–09 season. Following this, he admitted fears over his future at York after struggling to feature in the team, having only made two starts since April. It was confirmed in
Darren Kelly