Catherine was at the National Memorial Arboretum in Staffordshire for the ceremony, where the Last Post signalled the start of a two-minute national silence at 11:00 GMT to mark the end of the First World War.
Queen Camilla was at London's Paddington Station for a wreath-laying ceremony, having travelled there by train.
The Prince of Wales also delivered a video message for young people, sharing his thoughts on the importance of wearing a red poppy and saying that "remembrance is for everyone".
This was the first time Catherine had attended the service at the National Memorial Arboretum.
She laid a wreath at the centre of the Armed Forces Memorial, watched by a crowd including veterans and their families.
Catherine paused for a moment of reflection before returning to her seat, where she bowed her head as the crowd prayed for those affected by conflict.
The Prince of Wales's message was part of a virtual event for children aged nine to 14 in the UK.
In it, he says: "When we remember, we connect personally to service.
"We learn from the courage of others, and we carry their stories forward, so that they are not forgotten.
"It's not just about the past – it's about shaping who we become in the future.
"Remembrance teaches us empathy, resilience and responsibility.
"And when we wear a red poppy or observe a moment of silence, we are saying, 'Thank you. We have not forgotten, and we will not forget.'"
The Princess Royal is in Australia at Gallipoli Barracks.
Meanwhile, at the service in Staffordshire, a poem specially commissioned from the Arboretum's resident poet, Arji Manuelpillai, was recited. Mr. Manuelpillai said: “‘A Sonnet for Us All’ encapsulates the stories etched into the hundreds of memorials at the National Memorial Arboretum. It invites people to listen to, reflect on, and consider the emotions that inspired these sculptures.”
“These human connections, and the gentle responsibility to carry love forward, are themes that resonate not only with me, but also with the Princess of Wales, for whom the importance of service and compassion is particularly close to her heart.”
Queen Camilla joined passengers on the 09:28 train from Chippenham to Paddington, where a service of remembrance was held for military personnel and their families.
Later on Tuesday, William will join the King and Queen at Windsor Castle, where a reception will be held to honour veterans who served in the Pacific during the Second World War.
The event, which will also be attended by the Duke of Edinburgh and the Duchess of Gloucester, will continue the commemorations of the 80th anniversary of VJ Day – or Victory over Japan Day.
Elsewhere in the world, French President Emmanuel Macron attended a wreath-laying ceremony on the Champs-Élysées in Paris to mark the signing of the armistice agreement on the 11th day of the 11th month.
Meanwhile, the Princess Royal is in Australia and visited Gallipoli Barracks in Brisbane where she laid a wreath.
Accompanied by her husband, Sir Timothy Laurence, Princess Anne also met current and former armed forces personnel and their families.