McHugh made his senior international debut as a referee on 17 September 1994 when he took charge of a 1995 Rugby World Cup qualifier between Romania and Wales at Dinamo Stadium.
[3][4][8][9] On 18 February 1995 McHugh made his Five Nations Championship debut when he took charge of a match between France and Scotland at the Parc des Princes.
On 21 February 2004 he refereed his final Six Nations Championship game when he took charge of the match between England and Scotland at Murrayfield.
He made his Rugby World Cup debut on 3 June 1995 taking charge of a match between Canada and South Africa.
McHugh issued three red cards, sending off Canada's Rod Snow and Gareth Rees and South Africa's James Dalton following a brawl.
These incidents allegedly incited Pieter Van Zyl, a South African supporter, to invade the pitch and tackle and assault McHugh.
Van Zyl evaded over four hundred security officials to launch the assault as New Zealand's Justin Marshall was preparing to put the ball into a scrum.
New Zealand's Richie McCaw punched Van Zyl and, together with South Africa's AJ Venter, wrestled the assailant off McHugh.