Politicians, members of the royal family and veterans will commemorate those who lost their lives in a conflict later, while the United Kingdom marks Remembrance Sunday.
A two-minute silence will be held across the country at 11:00 GMT.
Boris Johnson, Jeremy Corbyn and Jo Swinson will separate from the election campaign to attend the annual ceremony at the Cenotaph in London.
Prince Charles will lay a wreath during the service in the name of the queen, who will watch over a balcony.
Also present will be the Duke and Duchess of Cambridge and the Duke and Duchess of Sussex, gathered on Saturday for this year's Royal Albert Hall Remembrance Festival.
The beginning and end of the two minutes of silence will be marked by the shot fired by King Artop Royal Horse Artillery.
Starting at the same time as the two minutes of silence, the Cenotaph service will honor the Armed Forces community, British and Commonwealth veterans, the allies who fought alongside the United Kingdom and the civilian military involved in both. world wars and later. Conflicts.
Ministers, religious leaders and representatives of Commonwealth nations will be present alongside hundreds of members of the armed forces.
The Duke of Cambridge and the Duke of Sussex will follow Prince Charles to lay wreaths.
An officer of the Royal House must lay a wreath in the name of the Duke of Edinburgh, who retired two years ago.
Five former prime ministers – Sir John Major, Tony Blair, Gordon Brown, David Cameron and Theresa May – are also expected to attend.
Once the wreaths are deposited, Mrs. Sarah Mullally, Bishop of London, will lead a service that will end with the sound of the Royal Air Force bell, Rouse.
After service, nearly 10,000 veterans will march slowly past the war memorial.
Veteran of the Second World War, Ron Freer, age 104 and blind, will be the oldest person to parade at the cenotaph this year.
Remembrance Sunday commemorations continue to be of "special importance" to him because his father was killed in 1918 and is buried at Dernancourt Communal Cemetery in the Somme, France, according to Blind Veterans UK.
Mr. Johnson stated that he would be "proud" to deposit his first crown at the Cenotaph as prime minister and pledged to continue to "defend those who are serving today with such courage." in our armed forces ".
He said in a tweet he would think of "the men and women who, over the centuries, have given so much to protect our country".
Union leader Mr. Corbyn said in a video message"We are all here today because we owe a lot to those who have gone before us, and today we remember them."
Many serving staff, veterans and their families "do not receive the support they deserve," he said.
And Liberal Democratic leader Swinson said people should take a break to reflect and remember how fragile peace can be.
The trio will be joined by Ian Blackford, leader of the SNP in Westminster, and Nigel Dodds of the DUP.
In addition, Scottish Prime Minister Nicola Sturgeon will lay a wreath at the memorial stone in Edinburgh City Chambers before giving a reading during service at St. Giles Cathedral.
- Prime Minister to lead Remembrance Events
- Wales marks the Sunday of remembrance
In Northern Ireland, Taoiseach Leo Varadkar is scheduled to attend a Remembrance Sunday ceremony in Enniskillen, County Fermanagh.
Ceremonies are also held across Wales, including at the Welsh National War Memorial in Cardiff.
This year marks the 100th anniversary of the Armistice Day celebration on November 11, 1919, with the first two-minute silence.
The Royal British Legion urged the country to suspend its daily activities to join the act of commemoration Sunday.
The ceremony at the cenotaph comes after Prince Harry, Meghan, Prince William and Kate joined the Queen at the Royal Albert Hall in London on Saturday for the Festival of Remembrance.
It was their first appearance as a band since Harry and Meghan declared that they were fighting against public life.