While Kelly was obviously well known to rebel and loyalist alike during the short duration of the Wexford rising, almost nothing is known of him outside this time. He was one of the leaders of the rebel victory at the Battle of Three Rocks which led to the capture of Wexford town but was later seriously wounded while leading a rebel column at the Battle of New Ross. Robert Gogan describes how Kelly was under orders from the Wexford commander Bagenal Harvey to attack the British outposts around New Ross but on no account to attack the town itself.
The rebels outnumbered the British forces and so Harvey sent a messenger to give them an opportunity to surrender.
The messenger was shot while carrying a white flag. This angered the rebels who began the attack without receiving the official order from Harvey.
Kelly’s column of 800 men attacked and broke through Ross’s "Three Bullet Gate" and proceeded into the town itself. After initial success, they were eventually beaten back by British troops and Kelly was wounded in the legal
He was moved to Wexford to recuperate but after the fall of Wexford on 21 June was dragged from his bed, tried and sentenced to death.
He was hanged on 25 June 1798 along with seven other rebel leaders on Wexford bridge, after which his body was decapitated, the trunk thrown into the River Slaney and the head kicked through the streets before being set on display on a spike.