The Queen and the President of Germany heard prayers for a time of "harmony" during the service, which marked the centenary of the Armistice. (Picture: PA)
President Frank-Walter Steinmeier and the Queen were joined by the Prime Minister, the Prince of Wales and Duchess of Cornwall, the Duke and Duchess of Cambridge and the Duke and Duchess of Sussex for the remembrance service.
Dean of Westminster, Dr John Hall, prayed for a time when conflict was "transformed into friendship and collaboration".
The Queen and Mr Steinmeier watched as flowers were laid at the grave of the unknown warrior, later shaking hands at the end of the service.
In his bidding, the dean said:
"As we mark today the centenary of the Armistice that brought to an end the First World War, we remember with sorrow the sacrifice of lives on all sides of the conflict and the suffering of the devastated and bereaved."
The choir of Westminster Abbey sang throughout the service, and readings were delivered by Theresa May and Prince Charles.
Mr Steinmeier delivered his reading in German near the end of the service.
Among the congregation was 88-year-old Ruth Gayfer, whose parents Edwin Oliver and Evelyn Boyce were in the First World War and wrote love letters to each other.
Ms Gayfer said her father enrolled when he was just 16 and was in the 4th East Yorkshire Regiment, while her mother was a nurse.
Mr Oliver died in 1934 when Ruth was just four.
Reflecting on events on Sunday, she said: "It's wonderful, it really is.
"My older sister is 97 and she's absolutely delighted because of course, she remembers him in her teens when he took her on cycling holidays and things like that."
Another member of the congregation was Patricia Barber, 73, from Ilford, whose grandfather, Private John Thomas Blackett, served with the 5th Battalion Dorset Regiment.
She said: "I'm very proud to be here to talk about my grandfather. He's a brave man. Although he wasn't actually killed in the war, I think as a result of his injuries is probably why he died.
"He was shell-shocked and discharged as unfit for active service and that was in June 1918, and then two months later he died tragically in a drowning accident.
"So whether that was because he was shell-shocked he fell in the river or jumped, we don't know. It was an open verdict.
"But he's got no marked grave and his name's not on any memorial, or even in the regimental roll of honour."
Ms Barber said her grandfather has a military medal, and she still hopes to see his name on a memorial or a headstone in future.
"It would be nice just to get his name on a memorial," she said.