Schools, offices and churches took part in the two minutes’ silence at 11am, marking the time when Allied Forces declared an end to fighting with Germany 97 years ago.
The Gurkhas were among regiments lining the street for a Whitehall ceremony, where singer Cerys Matthews read an extract from The Times newspaper from October 1915 about the deaths of 41 only-sons in battle.
The widow and son of murdered soldier Lee Rigby laid wreaths in Woolwich as the nation fell silent.
Jack Rigby and his mother Rebecca, who is originally from Halifax, attended a service at St George’s Chapel, where Fusiler Rigby’s name is engraved on a brass plaque, as millions of people remembered those killed in conflicts since the beginning of the First World War.
Fusilier Rigby, 25 was killed outside his barracks in Woolwich, south-east London, in May 2013 by two Islamic extremists.
A handwritten note on a wreath laid by his son Jack read: “To daddy, me and mummy miss and always love you.”
The Royal British Legion held its annual Silence in the Square event in Trafalgar Square, where actor Bernard Cribbins gave a reading of Rudyard Kipling’s poem Tommy.
The Queen marked the two minutes’ silence privately at Buckingham Palace with her family.
The Princess Royal attended Armistice Day commemorations at the National Memorial Arboretum in Staffordshire.
In Trafalgar Square, 91-year-old Second World War veteran Danny McCrudden sang The Impossible Dream to crowds gathered ahead of the silence.
The world’s last remaining Swordfish aeroplane dropped thousands of poppies over the remembrance service at St Bartholomew’s Fleet Air Arm Memorial Church in Yeovilton, Somerset.
Later today, 19 British veterans will be presented with the Legion d’honneur, France’s highest distinction, for their role in liberating France during the Second World War.
The medals will be presented by the French Ambassador Sylvie Bermann in a ceremony at her residence in Kensington, London.
More than 120,000 tributes were planted in Fields of Remembrance at Westminster Abbey and in Cardiff, Belfast, Gateshead, Edinburgh, Inverness and Lydiard Park near Royal Wootton Basset.
The Last Post was sounded by a bugler from the band of Her Majesty’s Royal Marines at the Imperial War Museum in London. A recital was also played on a violin made from sycamore and pine trees which grew in the former battlefields on the Western Front
Chelsea Pensioners observed the two-minute silence at Lloyd’s of London, where a remembrance ceremony was held on its trading floor.
At Holyrood, all parliamentary business was suspended as First Minister Nicola Sturgeon, MSPs, staff and visiting veterans joined the Presiding Officer in the building’s garden lobby for the Scottish Parliament’s commemoration.
Tricia Marwick closed the event with a reading of a poem, followed by MSP Stuart McMillan piping All The Blue Bonnets Over The Border to commemorate 100 years since the Battle of Loos.
The silence was observed at the Royal Courts of Justice in London - which houses the High Court and Court of Appeal.
Some judges suspended hearings shortly before 11am so that lawyers and members of the public could stand in silence outside courtrooms. Others halted proceedings at 11am but remained in court.
The Princess Royal, wearing three poppies on the shoulder of her overcoat, read a passage from the Bible during the service at the Armed Forces Memorial.
Following the service, attended by around 500 people, Anne was shown some of the 16,000 names carved into the Portland stone memorial, commemorating service personnel killed in the line of duty since 1948.
D-Day veteran Ken Todd, from Oswestry in Shropshire, was visiting the memorial for the first time for the first time.
The 90-year-old, who served on gunboats which delivered around 250 engineers to Sword Beach, said Armistice Day and similar commemorations were always highly emotional for veterans.
The former Royal Marine only discovered at a D-Day commemoration in 2009 that all the engineers he helped to land on Sword Beach had survived.
Speaking after the service in Alrewas, Staffordshire, the veteran said: “On the 65th anniversary of D-Day I went back over there and I was told all the engineers got out.
“That was very, very emotional for me.”