Canadian ambassador Kevin Vickers tackles protester at Easter Rising event in Dublin
In his previous role as the sergeant-at-arms in the Canadian parliament, Kevin Vickers shot dead a gunman who rampaged through the building in 2014.
He was the first to intervene at Thursday's event in Dublin.
It was attended by members of the British and Irish armed forces.
Irish Foreign Affairs Minister Charlie Flanagan and the British ambassador Dominick Chilcott were also present at the event in Grangegorman Military Ceremony.
It was reported that during speeches the protester jumped up from seating reserved for invited guests and shouted that the ceremony was an "insult".
Irish state broadcaster RTÉ said Mr Vickers was able to pull the protester away before the man was handcuffed and arrested by police.