Hundreds of people gathered in the Garden of Remembrance and on the streets outside as members of the armed forces and representatives from associated organisations participated in the service to remember those who died in conflict.
Ms O’Neill’s laurel wreath bore a card with the words: “Today, as First Minister, I remember all lives lost in the horror of war and conflict.
“Through understanding and respect for our differences, we can build a stronger, more compassionate, and united society.”
Emma Little-Pengelly lays a wreath at City Hall today. Pacemaker
Ms O’Neill last year became the first senior Sinn Fein figure to take part in such an event in Northern Ireland.
On Thursday she announced she would also attend this year’s ceremony.
Ahead of the event this morning, Ms O’Neill said: “From my first day in office, I made a commitment to be a First Minister for all and I am fully committed to delivering on that promise.
“Today, I will attend an event at Belfast City Hall to remember all those who lost their lives during the First World War and in subsequent conflicts.
“As First Minister, it is my responsibility to acknowledge and show respect for all traditions and perspectives in our society.
“I also bring my own lived experience, political perspective, and aspirations for Irish unity, as a proud Irish Republican.
“And while we may not agree on everything, we must find common ground in respecting each other’s traditions and perspectives.
Michelle O’Neill lays a wreath at the cenotaph. Pacemaker
“Our people have travelled a long road to peace. But peace is not a single moment in time, it is a journey. I will continue moving forward, taking the necessary steps even when difficult, because it is the right thing to do for our people and communities.
“Politics must give hope to the next generation, ensuring our children and grandchildren grow up in a much better world than we did.
“We are living in a time of enormous change on our island, and that requires positive leadership, and I will not shy away from that responsibility.”
There had been some speculation that Ms O’Neill might not attend the event this year in the wake of the DUP’s behaviour following Soldier F’s acquittal of murder and attempted murder on Bloody Sunday.
Party leader Gavin Robinson posted an image of the Parachute Regiment insignia on social media, causing widespread anger across nationalism.
Last month Belfast Crown Court ruled the evidence against Solider F fell well short of what was required for conviction.
The DUP leader’s decision to tweet the Parachute Regiment’s insignia following the verdict was condemned as extremely insensitive to the victims.
Ireland’s Minister for Education and Youth, Helen McEntee, and Lord Mayor of Belfast Tracy Kelly also laid wreaths in Belfast on Sunday.
Senior TUV figure Ron McDowell did not attend the event at Belfast City Hall for a second year in a row because of the presence of Ms O’Neill.
Tracy Kelly, the Lord Mayor of Belfast, lays a wreath. Pacemaker
Other events are taking place across Northern Ireland, and also in Dublin, to mark the 107th anniversary of the armistice that ended the First World War.
Taoiseach Micheal Martin attended a service in Enniskillen where he laid a wreath at the town’s war memorial.
His wreath read “in remembrance on behalf of the Irish Government”.
Secretary of State Hilary Benn also attended as the 80th anniversary of the end of the Second World War was also commemorated.
Saturday marked the 38th anniversary of a bomb explosion before a Remembrance Day service in Enniskillen, which killed 11 people. A 12th died some years later.
Northern Ireland Secretary Hilary Benn, Head of the Northern Ireland Civil Service Jayne Brady and Taoiseach Micheal Martin in Enniskillen. Liam McBurney
DUP Leader Gavin Robinson was in London at the National Service of Remembrance at the Cenotaph to lay a wreath at the monument.
DUP leader Gavin Robinson lays a wreath in London. Yui Mok/PA Wire
King Charles III led a two-minute silence at the service and also laid a wreath.
He was joined by other senior royals and political leaders, including Prime Minister Sir Keir Starmer and Conservative Party leader Kemi Badenoch at the ceremony.
Charles took centre stage and laid the first wreath at the Cenotaph in recognition of the fallen from conflicts dating back to the First World War, and was followed by the Prince of Wales.
The King, wearing Field Marshal uniform with a ceremonial frock coat, saluted before stepping back from the monument after leading a two-minute silence at the annual Remembrance Sunday service in London.
The King was followed by the Prince of Wales during the Remembrance Sunday service at the Cenotaph (James Manning/PA)
His son, dressed in Royal Air Force uniform in the rank of Wing Commander, also saluted after laying his wreath at the Cenotaph.
First Minister Michelle O’Neill and Deputy First Minister Emma Little-Pengelly.
Michelle O’Neill lays wreath at Cenotaph in Belfast on Remembrance Sunday
William, who in 2013 completed seven-and-a-half years of full-time operational military service, promotes the roles and welfare of current and former service personnel as a key part of his work.
Sir Keir also laid a floral tribute, along with senior politicians including Ms Badenoch, Sir Ed Davey, Yvette Cooper, Shabana Mahmood and Sir Lindsay Hoyle and representatives from the Commonwealth.