The Queen and senior royals are attending a concert at the Royal Albert Hall on the eve of Armistice Day.
The annual Festival of Remembrance in London, which commemorates the war dead, will include performances from Sir Tom Jones and Sheridan Smith.
It comes ahead of Remembrance Sunday on 11 November, which this year marks 100 years since the end of World War One.
The dukes and duchesses of Cambridge and Sussex, and Prime Minister Theresa May are among the audience.
The event has been organised by armed forces charity the Royal British Legion as a “thank you to all who served, sacrificed and changed our world” and will be broadcast later on BBC One on Saturday.
The concert will also see performances from Welsh singer Bryn Terfel as well as former McFly stars Tom Fletcher and Danny Jones who will deliver a song written to celebrate the RAF centenary.
British cellist Sheku Kanneh-Mason, who won BBC Young Musician of the Year in 2016, and the Kingdom Choir, who performed at Prince Harry and Meghan’s wedding, will also perform.
Earlier, the Duke of Sussex laid a wreath at Twickenham ahead of England’s rugby Test match against New Zealand.
Media playback is unsupported on your device
Prince Harry was joined by New Zealand Deputy Prime Minister Winston Peters to lay their wreaths, before the Last Post was played and spectators joined in a minute’s silence.
The prince also met the descendants of two former England captains who died in the war.
Also on Saturday, a candlelit vigil will be held at the National Memorial Arboretum.
The Armistice 100 years on
Long read: The forgotten female soldier on the forgotten frontline
Video: War footage brought alive in colour
Interactive: What would you have done between 1914 and 1918?
Living history: Why ‘indecent’ Armistice Day parties ended
The concert comes as French President Emmanuel Macron and Germany’s Chancellor Angela Merkel visited the town of Compiègne in northern France, where the Allies and Germany signed the Armistice.
On Friday, Mrs May visited Belgium with the country’s prime minister and laid wreaths at the graves of the first and last UK soldiers killed in the war.
She later visited a World War One cemetery in France with Mr Macron.
Poppy displays have been created across the country, including in a street dubbed “Poppy Road” in Walsall and at Hertford Castle.
What is planned for Armistice Day on Sunday?
Sunday will see commemorations around the world for the Armistice Centenary.
In the UK, pipers across the country will begin the commemorations at 06:00 with “Battle’s O’er” – a traditional Scottish lament played at the end of battle.
The Queen and senior royals will attend London’s Cenotaph for the national remembrance service at 11:00 GMT.
And, for the first time ever, it will be followed by a procession of 10,000 members of the public past the Cenotaph where wreaths will be laid.
London’s Big Ben will also strike on Remembrance Sunday, taking a break from its ongoing renovation work.
Services are also taking place elsewhere in the country including in Edinburgh, Glasgow, Cardiff, Belfast and Chichester.
In the evening, 1,000 buglers will sound the Last Post at spots around the country before 1,000 beacons will be lit to mark a return to the light of peace.
More than 1,000 cathedrals and churches will ring their bells at the same time at 19:05.
The Queen and senior royals will also attend an evening service of remembrance at Westminster Abbey.