The Bruff man makes his officiating debut in the competition for the clash of New Zealand and Tonga in Auckland on September 9.
Clancy last night said: “I am delighted. It is something I have been working towards for years and it makes all that effort worthwhile.
“It is a huge honour to be selected for the World Cup and it is incredible to be getting the opening game. I only got the news this week so it is still sinking in for me and for my family.
“Hopefully Bruff can win the Bateman Cup final today against Dungannon and make it a cause for double celebration!”
Clancy also revealed he will be also taking charge of a Tri Nations game between South Africa and New Zealand in August in Port Elizabeth.
He is joined by fellow Irish whistleblower Alain Rolland on the 10-man panel announced by the IRB after a meeting in Dublin this week.
The remaining places are filled by English duo Wayne Barnes and Dave Pearson, Frenchman Romain Poite, South African pair Jonathan Kaplan and Craig Joubert, New Zealand’s Bryce Lawrence and Australian official Steve Walsh.
The group will preside over all 48 ties, supported by seven assistant referees and four television match officials.
Among the assistant referees are Simon McDowell (Ireland), Stuart Terheege (England), Tim Hayes (Wales) with assistants Jerome Garces (France) and Chris Pollock (New Zealand) also acting as reserve match referees.
Full appointments for the pool games will be announced by the IRB in August.
Among the names not included are Ireland’s Alan Lewis, Australian Stuart Dickinson, plus South Africans Marius Jonker and Mark Lawrence.