The Queen watched on for the first time in her 65-year reign as Prince Charles led Remembrance Sunday commemorations at the Cenotaph in Whitehall.
In a break with tradition, Prince Charles laid the head of state's wreath at the base of the monument shortly after a two-minute silence at 11am.
The Queen appeared to wipe away a tear as she watched the service from a Foreign Office balcony with the Duke of Edinburgh and Duchess of Cornwall.
The change of protocol is seen as one of the Queen's most significant handovers of Royal responsibilities to the heir to the throne.
Placing the wreath at the base of the Whitehall monument would have required the monarch, who is 91, to walk backwards down the stone steps.
As well as laying the head of state's wreath, Charles laid his own wreath at the base of the Cenotaph.
The Duke of Cambridge, Prince Harry, the Duke of York, the Earl of Wessex, the Princess Royal and the Duke of Kent also laid wreaths.
Charles has stepped in for the Queen at the ceremony twice before - in 1983 when she was in Kenya and in 1999 when the monarch travelled to South Africa.
Across the rest of the country, millions honoured Britain's war dead at other Remembrance Day commemorations.
Irish Prime Minister Leo Varadkar, Northern Ireland Secretary James Brokenshire and DUP leader Arlene Foster laid wreaths at the cenotaph in Enniskillen, County Fermanagh - 30 years since an IRA bombing there killed 12 on Remembrance Sunday.
Meanwhile, a suspicious object found close to a war memorial in Omagh, County Tyrone, was a viable pipe bomb device, say police.
It has been taken away by officers for further examination.
PSNI Chief Constable George Hamilton said: "This small but potentially dangerous device was left to cause the maximum amount of disruption to the Remembrance Sunday commemorations.
"This is the action of a small and callous group of violent people who have nothing to offer our communities other than fear and intimidation."
The alert forced the diversion of a parade and the cancellation of wreath-laying.
In August 1998, a Real IRA bombing in Omagh claimed 29 lives and was the biggest single atrocity during the Troubles in Northern Ireland.
On Saturday, the Queen and senior royals joined servicemen and women past and present at the annual Festival of Remembrance as the nation remembered its war dead on Armistice Day.
The monarch was joined at the Royal Albert Hall in London by thousands of veterans for the 90th anniversary of the event, organised by the Royal British Legion, of which she is patron.