Published Monday, 11 November 2013
A two-minute silence was observed at 11am on Monday to mark the end of the First World War - on the eleventh hour, on the eleventh day, of the eleventh month.
Mr Ó Muilleoir made history as he stood alongside DUP politicians for the tribute.
Afterwards he said he felt the gesture was an important part of his efforts to be a mayor "for all the people of Belfast", as he promised when taking office.
The Sinn Féin man said: "Part of that means reaching out to unionism and today really was about peacemaking towards unionism.
"This is a huge event in the unionist calendar in particular and I wanted to show respect for unionist people and the Protestant people of Belfast by being at the cenotaph on the 11th hour of the 11th day of the 11th month."
However he added that the decision had not been easy.
Mr Ó Muilleoir said: "I think it's the most difficult decision I have made in 30 years in politics and community activism. It is a challenge and I think that it had to be done.
"I think the peace and building the peace and building a better Belfast demands that we have to move ourselves into places where we are uncomfortable, which challenge us and which move us into new positions of peacemaking."
President of the Royal British Legion, Mervyn Elder, said it was an important day.
He told UTV: "As far as we are concerned we think it is very nice that the First Citizen honoured us with his presence today and helped us in a significant act of remembrance."
Democratic Unionist deputy mayor Christopher Stalford joined Ó Muilleoir as crowds gathered near the Cenotaph for the act of remembrance.
He welcomed the Lord Mayor's attendance.
DUP councillor Mr Stalford added: "I had always intended to be going to Armistice Day and I am pleased that the lord mayor made the decision that he wanted to go too."
"I think that was a positive and forward step and I hope it is a first step towards Sinn Féin embracing remembrance and all of the events that take place around that."
Ulster Unionist leader Mike Nesbitt also welcomed the move.
He said: "I also hear that the Lord Mayor of Belfast, Cllr Máirtin Ó Muilleoir, attended the Armistice service at Belfast City Hall, thus becoming the first Sinn Féin representative to take part in an Armistice Day ceremony at City Hall.
"I consider these gestures important at a time when a generosity of spirit will be required from all political leaders, if we are to succeed in our current efforts to reach agreement on the difficult issues under consideration in the Haass talks process."
In the past Sinn Féin has boycotted November's events due to the association with the British military - but members have laid wreaths for the Battle of the Somme on 1 July.
It comes after First Minister Peter Robinson, along with the Tánaiste Eamon Gilmore, were among the dignitaries paying tribute to those who died in conflict on Remembrance Sunday.
Wreaths were laid during a service at the Cenotaph at Belfast City Hall.
Meanwhile in Enniskillen the Taoiseach, Enda Kenny, joined NI Secretary of State Theresa Villiers part joined those marking the national day of remembrance in the town.
Twenty-six years ago, 11 people were killed and over 60 were injured in an IRA bomb at the town's War Memorial.
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