The service follows a host of Remembrance events members of the Royal family have attended throughout the week.
Armistice Day 2018 marks 100 years since the Armistice was signed, ending the First World War and so Remembrance 2018 is a particularly important and poignant year, with a number of extra commemorative events.
Last night Harry and Meghan joined the Queen and other members of the Royal family at Royal Albert Hall for the deeply moving Festival of Remembrance. This morning, they were at the Cenotaph for Remembrance Sunday service.
A video of the arrivals.
Kensington Palace shared this beautiful image from the abbey before the royals arrived.
The service is the finale of a day of national events to commemorate Armistice Day.
The Prince of Wales and the Duchess of Cornwall arriving.
The Duke and Duchess of Cambridge.
President of Germany Frank-Walter Steinmeier and his wife Elke Büdenbender. Meghan joined the first lady on the balcony of the Foreign Office. It was a historic day marking the first time a representative of Germany has laid a wreath at the Cenotaph.
Meghan greets Prime Minister Theresa May.
The Queen and the President of Germany placed fresh flowers at the Grave of the Unknown Warrior. The flowers are brightly coloured to symbolise celebration, and include heather, gerbera, lilies, roses and chrysanthemums.
The Grave of the Unknown Warrior (often known as 'The Tomb of the Unknown Warrior') holds an unidentified British soldier killed on a European battlefield during the First World War. He was buried in Westminster Abbey, London on 11 November 1920, simultaneously with a similar interment of a French unknown soldier at the Arc de Triomphe in France, making both graves the first to honour the unknown dead of the First World War. In May, Meghan's wedding bouquet was sent to the abbey and placed on the Grave of the Unknown Warrior. This is a tradition which was begun by HM Queen Elizabeth, the Queen Mother, after her marriage to King George VI in memory of her brother Fergus who was killed in 1915 at the Battle of Loos during the First World War.
The Sussexes and the Cambridges walk past the grave.
Nine young people placed flowers at the Grave of the Unknown Warrior. The nine have been involved in commemorative events over the past four years, researching the lives of members of the Armed Forces who served during WW1.
Harry and Meghan take their seats.
Other royals in attendance included the Duke and Duchess of Gloucester, the Duke of Kent and Prince Michael of Kent
Actor Sophie Okonedo OBE read from the diary of socialist Beatrice Webb, 11th November 1918: "Peace! London to-day is a pandemonium of noise and revelry, soldiers and flappers being most in evidence..."
The Prime Minister read Isaiah 58: 6-12: "Is not this the fast that I have chosen? To loose the bands of wickedness, to undo the heavy burdens, and to let the oppressed go free, and that he break every yoke?"
German President Frank-Walter Steinmeier read 1 St John 4: 7-11 in German. Below, the English translation from the Order of Service.
During his address, the Archbishop of Canterbury said: "The final verdict on evil is defeat...On this day we remember, in order to act...Enemies have reconciled and that is hope for the world."
The Prince of Wales read St John 15: 9-15: "Greater love hath no man than this, that a man lay down his life for his friends."
The royals joined in singing hymns.
Click here to view the Order of Service in its entirety.
Her Majesty shakes hands with the German president marking the end of the service.
The Palace shared this lovely image of William, Kate, Harry and Meghan.
The Duke and Duchess departing.
It is Prince Harry's second visit to Westminster Abbey this week. On Thursday, he opened the Royal British Legion's 90th Field of Remembrance.
Each November the Royal British Legion establishes a Field of Remembrance in the grounds of the Abbey. The field is a sea of remembrance crosses with scarlet poppies - a symbol of remembrance and a tribute to the memory of ex-service men and women.
Row upon row, with their scarlet poppies, around 70,000 crosses carry personal messages to those who lost their lives in service of our country. It was undoubtedly a very moving visit for Harry who served in the army for ten years, undertaking two tours of Afghanistan.
The Duchess looked elegant in a navy belted skirt suit for the event. Generally during royal engagements, the Palace release details on designers the Duchess is wearing. Naturally, given the sombre nature of Remembrance events that is not the case during Remembrance weekend. As the look is quite possibly bespoke, if the designer does not claim credit for it, it's unlikely it will become known unless the look is worn again.
As several of you correctly noted, there are strong design similarities between the look and the Prada skirt suit Meghan wore for the Queen's Young Leaders Awards in June.
Meghan has added a pair of her favourite Aquazzura Deneuve bow pumps to her collection in navy.
A product shot of the pumps in black.
The Duchess wore a black beret style hat. It's very likely a Stephen Jones creation.
Heaven correctly noted it's almost identical to the Stephen Jones beret Meghan wore for the Commonwealth Day service.
Meghan's navy clutch is an unidentified one she's carried several times.
If you're just joining us, click here to read this morning's Remembrance Sunday post.
The week has been filled with deeply touching tributes to those who made the ultimate sacrifice. I was very pleased to see the Royal family involved in so many elements of it, and to see Meghan attending several events in her first Remembrance week. We will never forget.
We'll see Harry and Meghan at Prince Charles' 70th celebrations on Wednesday night. I'm hoping a family portrait is released from the event.