He was born circa 1769 into an old landowning Wexford family, the son of Thomas Francis Colclough and lived at Ballyteigue, Kilmore. He went abroad to study medicine and qualified as a doctor. On his return to Wexford he married Elizabeth Berry.
He became involved in Irish nationalism, joined the United Irishmen and was arrested with Lord Edward Fitzgerald on 27 May 1798 and taken to Wexford gaol. From there he was sent with Fitzgerald to parley with the rebels at Vinegar Hill, returning alone to report negotiations had failed. He was later, somewhat reluctantly, in the company of the rebels at the Battle of New Ross.
After the battle, and the royalists had regained the town, he fled with his wife and Bagenal Harvey to the Greater Saltee Island, from whence they planned to escape to republican France. They were betrayed under torture by a local farmer, arrested, and brought to Wexford town to be court-martialled.  Found guilty, they were hanged on Wexford bridge on 28 June 1798, their heads afterwards put on spikes and their bodies thrown into the River Slaney. Colclough’s body was recovered by his supporters during the night and buried in St. Patrick’s burying ground, Wexford. (Source)