Jo Cox’s husband condemned his wife’s death as an “act of terror” as he fought back tears in an emotional tribute in Trafalgar Square.
Thousands of people gathered in London to remember the Labour MP on what would have been her 42nd birthday, as similar events took place across the UK and around the world.
“Jo’s killing was political, it was an act of terror designed to advance an agenda of hatred towards others,” Brendan Cox told the crowd.
“What a beautiful irony it is that an act designed to advance hatred has instead generated such an outpouring of love.
“Jo lived for her beliefs and on Thursday she died for them, and for the rest of our lives we will fight for them in her name.”
His speech was overshadowed by the droning of a plane carrying a banner with a Vote Leave slogan that repeatedly passed over the crowd, flying low enough for its writing to be read.
The Labour MP Stella Creasy was among the attendees condemning the “disgusting” timing, although it was not clear whether the plane’s path was deliberate.
Its engines could be heard as Mr Cox described his wife’s passionate campaigning for Britain to remain in the European Union.
“Today would have been Jo’s 42nd birthday and she would have spent it dashing around the streets of her hometown trying to convince people that Britain is stronger in Europe,” he said.
“She feared the consequences of Europe dividing again, hated the idea of building walls between us and worried about the dynamics that could unleash.”
A minute’s silence was held during the hour-long celebration of her life, which was also attended by her three-year-old daughter Lejla and son Cuillin, five.
Ms Cox’s younger sister, Kim Leadbeater, then took to the stage to pay tribute to the “caring, compassionate and inspirational” MP.
"We have been truly overwhelmed by the outpouring of kindness and support and it has provided great comfort and strength in order for us to keep going,” she said.
"I don't have any answers as to why such a horrendous and tragic event has occurred in our lives. But I do know that Jo would not have wanted any of us to allow it to make her life anything other than the force for good it always was.”
Malala Yousafzai, the education campaigner who was shot in the head by the Taliban for her activism, was among the guest speakers at the rally.
Events were being held in a variety of locations in tribute to Ms Cox's “love, energy, passion, flair, Yorkshire heritage and belief in the humanity of every person in every place”.
Bill Nighy performed a reading, while U2 recorded a musical tribute in Los Angeles.
The band that played at Ms Cox’s wedding, Diddley Dee, also played and a group of the MP's friends formed an honour guard dressed in suffragette-style sashes.
Leaders of multiple faiths were to lay 42 white roses, the symbol of Yorkshire, to mark her birthday at the event, hosted by Mrs Cox's friend Mariella Frostrup.
International events were also taking place in Beirut, Brussels, Melbourne, Nairobi, New York and Washington DC.
Glastonbury's Park Stage was the location of one tribute, while a charity album of music recorded by bands including Coldplay and Muse at the festival this weekend will be released in her honour.
Mr Cox said his wife would have been “amazed, baffled and humbled” at the global reaction to her death and the “outpouring of love from around the world”.
"Thank you for the love that you have poured on our family since our world collapsed on Thursday,” he said.
"As amazing and deeply touching as all of this is, I wish I wasn't here today. Not because I'm ungrateful to the organisers and you all for coming, but because of course I'd rather be with Jo.
"But I wanted to come and show my gratitude and that of all of our family.”
Wednesday’s commemorations came after a fundraising page in Mrs Cox's memory raised more than £1m for three of her favourite charities in just three days.
Tommy Mair, 52, has been charged with murdering Mrs Cox in a shooting and stabbing attack in Birstall last Thursday, and remains in custody.