He is the son of Anne and Alphonsus Donnelly; he has six older siblings named Dermott, Moira, Camelia, Eamonn, Patricia, and Martin. In 2015, he married Ali Astall. They welcomed a daughter named Isla in 2018. In 2022, they welcomed a second a child (a son named Jack).
He teamed up with Anthony McPartlin to become one of the most well-known television presenters in Britain's history.