During his career fighting for the national team he won a bronze medal at the flyweight division during the 1993 World Championships in Tampere, Finland.

The bronze medal Kelly won at the European Championship in Vejle gave him automatic qualification for the 1996 Summer Olympics in Atlanta, US, where he reached the quarter-finals.

His results were: Kelly, under the mentorship of Mickey Hawkins, then turned professional in September 1997, gaining a victory in his debut fight at the Ulster Hall in Belfast, with a first-round knockout (KO) over Chris Thomas on a card that included Steve Robinson, Julius Francis and fellow Northern Irishman Neil Sinclair.

Kelly was leading on points when the fight was stopped in the sixth round due to cuts.

[4] Kelly returned to the ring five months later and won the WBC International super-flyweight title against Igor Gerassimov.

Kelly's winning streak continued with a further addition to his record when he added the lightly regarded WBF flyweight title in May 2002.

After a win over Jovy Oracion in October 2002, Kelly was then out of the ring for almost a year and only returned in September 2003 to an unexpected fight against Irene Pacheco at the Salón Jumbo del Country Club, Barranquilla, Atlantico, Colombia for the IBF flyweight title.

[7][8][9] In April 2006, Kelly challenged Simone Maludrottu at the Andersonstown Leisure Centre in Belfast.

[1][10][11] Maludrottu was the naturally bigger man and carried more power, having fought at bantamweight for the majority of his career, however Kelly possessed the faster hands and higher technical ability.