Following the death of his mother, Queen Elizabeth II, King Charles will lead the Remembrance Sunday service at the Cenotaph for the first time as monarch.
At 11:00 GMT, the United Kingdom will observe two minutes of silence to pay tribute to the war dead.
Remembrance Sunday was one of the most important royal engagements in the late Queen’s calendar.
The King, politicians, and religious leaders will lay wreaths at the central London memorial.
King Charles’ ring of poppies will incorporate a ribbon of racing colours in a tribute to the ones used by the late Queen and his grandfather King George VI.
During his time as Prince of Wales, King Charles represented the late Queen at the last five Cenotaph services and laid a wreath on her behalf, as she watched from the Foreign Office balcony that overlooks Whitehall.
The beginning of the silence will be marked by Big Ben striking 11 times at 11:00.
The bell has been largely silent for five years after it was dismantled and repaired in a renovation project. While it has run for events such as New Year’s Eve and the late Queen’s funeral, its tolling on Sunday will mark its official return to use.
The service, led by the Bishop of London, will also feature a march past by 10,000 Royal British Legion veterans, representing 300 different Armed Forces and organisations between them.
Among those taking part will be World War Two veterans – fewer in number as each year goes by – and those who have served in more recent conflicts.
To commemorate 40 years since the Falklands War, 400 members of the South Atlantic Medal Association will also take part.
They will be joined by those who have lost loved ones in conflict, with the youngest marcher just eight years old.
A further 10,000 members of the public will line Whitehall to watch the service.
Along with King Charles, Camilla the Queen Consort, the Prince and Princess of Wales, the Earl and Countess of Wessex, Princess Anne and Vice Admiral Sir Tim Laurence, the Duke and Duchess of Gloucester, the Duke of Kent and Princess Alexandra, will attend the service.
The event will also be attended by senior members of the government.
Speaking ahead of the service, Prime Minister Rishi Sunak and Defence Secretary Ben Wallace commemorated the fallen and also paid tribute to those fighting for Ukrainians’ freedom.
Mr Sunak said: “This year more than ever, we are reminded of the huge debt of gratitude we owe those who lay down their lives to protect their country.
“As we fall silent together on Remembrance Sunday, we will honour the memories of the men and women we have lost and pay tribute to the brave soldiers of Ukraine as they continue their fight for freedom.”
His words were echoed by Mr Wallace, who said Remembrance Sunday was a time to reflect on the sacrifices made by our veterans and service personnel around the world.
“We must never forget those who gave their lives in defence of our values and our great nation,” he said.
“All of us will also be thinking of those brave Ukrainians who are fighting for their very own survival to defend freedom and democracy for all, just as the UK and Commonwealth soldiers did in both world wars.”
More than 100 Falklands War veterans and family members of those who died in the war will take part in a remembrance service and parade in the capital Stanley on Sunday.
They made the 8,000 miles (12,900km) journey via a special flight arranged by the Ministry of Defence, with many of the veterans making an emotional return to the Falklands for the first time since the war with Argentina broke out in 1982.
Over the past few days the veterans, along with mothers, wives and children of those who died, have visited the battlefields where British forces fought, with some shedding tears and placing crosses at cemeteries for fallen comrades and family members.
On Saturday, members of the Royal Family attended the annual Royal British Legion Festival of Remembrance at the Royal Albert Hall.
On Friday, the UK held another silence on Armistice Day to commemorate the end of World War One in 1918.