The honour will be bestowed on the 73-year-old next month in recognition of "his immense contribution to rugby and for overseeing the delivery of the most successful Rugby World Cup to date as chairman of Rugby World Cup Ltd."
The formal acceptance ceremony has been arranged for Millar's family, friends and colleagues from rugby in his home town of Ballymena. Eaton Park, the home of the Braidmen with whom Millar first made his mark, will be the place to be on December 12 when he receives the honour.
The 37-times capped Millar will be remembered as one of the game's great administrators. He represented Ireland as a player, coach and manager, and was elected President of the Irish Rugby Football Union in 1995 after 10 years of service.
He is standing down as chairman of the IRB next month and his wish to hold the acceptance ceremony at his old club has been granted. While a veritable who's who of the rugby world will travel to the ceremony, one of the biggest attractions is sure to be the Webb Ellis trophy, which will be on display in the clubhouse.
Ballymena RFC will also host a full IRB committee meeting the previous day, which will include discussions about the possible introduction of some new rugby laws.
The Legion d'Honneur was established by Napoleon Bonaparte in 1802 to reward both soldiers and civilians for exceptional merit or bravery.