It is the second time that protesters seeking a final say on the Brexit deal have descended on the capital, after 700,000 attended a similar march in October last year.
A number of famous faces have added their voice to both sides of the debate, with pro-EU celebrities including JK Rowling, Patrick Stewart, David Beckham, Billy Bragg, Paloma Faith, Daniel Craig, Bob Geldof and Elton John.
More than four million people have now signed an online petition demanding that Article 50 be revoked so the UK can remain in the EU.
Celebrities who still wish to leave the EU include Roger Daltrey, Sir Michael Caine and Elizabeth Hurley.
Here's a look at what other culture stars have said about Brexit.
Sir Patrick Stewart: The X-Men star has been vocal about his anti-Brexit views and is among the supporters of a second referendum. He is funding transport from Huddersfield and said: "The Put it to the People march may very well be our last chance to demand a democratic final say on this mess before it's too late".
Delia Smith: The celebrity chef has called Brexit a "dog's dinner" and was one of the stars who addressed crowds at the march in October. She has been helping to fund transport for marchers to attent the London rally.
Olly Alexander: Years and Years frontman Olly Alexander called Brexit "extremely harmful" and attended October's rally.
Steve Coogan: The Alan Patridge actor called Brexit a "looming disaster" and has previously funded coaches to help protesters travel from Manchester to London to join the march last year. In February he said Brexit was why hapless TV presenter Partridge had returned to the BBC.
Paloma Faith: The singer and actor signed the Revoke Article 50 petition and signalled her intention to join protesters marching in London today.
Nadine Shah: The Mercury Prize-nominated artist shared a photo of herself at the march with a placard bearing the words: "Music 4EU."
Billy Bragg: Nadine Shah was joined at the People's Vote March by fellow Music 4EU campaigners Billy Bragg and Fatboy Slim
David Beckham – The former captain of the England international football team announced on Instagram that he was “voting to Remain”. He said: “We live in a vibrant and connected world where together as a people we are strong. For our children and their children we should be facing the problems of the world together and not alone.” His wife, Victoria, has also announced her support for Remain.
Among other sportspeople to announce their intentions to vote Remain were former Gary Lineker, Olympic athlete Paula Radcliffe, former England rugby stars Brian Moore and Lawrence Dallaglio, darts player Bobby George, and OIympic gold medal sailor Ben Ainslie.
Elton John: The singer announced his intention to vote Remain on Instagram in 2016, sharing an image with the words “build bridges not walls” along with the caption: “I'm voting to remain. #StrongerInEurope”
Others in the music industry in support of Remain are Billy Bragg, Jarvis Cocker, Simon Cowell, Sir Bob Geldof and Florence Welch.
• JK Rowling – The author of the Harry Potter books has expressed concern that "racists and bigots" are directing parts of the Leave campaign. In a blog post, she added: “How can a retreat into selfish and insecure individualism be the right response when Europe faces genuine threats, when the bonds that tie us are so powerful, when we have come so far together? How can we hope to conquer the enormous challenges of terrorism and climate change without cooperation and collaboration?”
• Benedict Cumberbatch and Sir Patrick Stewart led more than 280 figures from the arts world who backed a vote to stay. An open letter pledging support for Remain was also signed by music stars Hot Chip, alt-J and Paloma Faith, authors Dame Hilary Mantel and John le Carre, and fashion designer Dame Vivienne Westwood.
Daniel Craig was pictured wearing a vote Remain t-shirt with the words "No man is an island. No country by itself" emblazoned across it in a picture tweeted on the Stronger IN account.
Other actors to voice support were John Hurt, Idris Elba, Helena Bonham-Carter, Game Of Thrones actor Daniel Portman, Keira Knightley and Cara Delevingne.
• Sir Stephen Hawking – The late physicist was in favour of remaining in the EU, and said "progress comes from co-operation". He said: "By working together in Europe we make our economy stronger and we give ourselves more influence in the world and we provide future opportunities for young people." Numerous scientists have also voiced their support for Remain, claiming an out vote would badly damage the field.
• Bear Grylls – The adventurer and TV presenter said he spoke "from the heart" in backing the EU. "At such a time for the UK to retreat, run and cut ourselves loose from Europe, when there are so many challenges on our doorstep, to me just doesn't feel either courageous or kind,” he said. “Europe has many flaws, but I also believe the way to help resolve many of those tough issues is from within... I have never been a good quitter and I am so proud of the UK and our values: tolerance, kindness, respect, courage and resilience. This is why I want us to stay together and Remain in Europe.”
Hugh Grant: The Four Weddings star signed the petition to Revoke Article 50 and said: "I've signed. And it looks like every sane person in the country is signing too. National emergency."
• John Cleese – The Monty Python star signalled he will vote to leave the EU when he tweeted: "If I thought there was any chance of major reform in the EU, I'd vote to stay in. But there isn't. Sad."
• Roger Daltrey – Former frontman of iconic rock band The Who wrote in The Mirror: “Whatever happens our country should never fear the consequences of leaving. We went into the Common Market in 1973. Do you know what was going on before we went in? It was the 1960s. The most exciting time ever - Britain was Swinging. Films, Theatre, Fashion, Art and Music. We were the World leaders. You had Harold Pinter, The Beatles, John Osborne, Mary Quant, The Stones, Queen... and The Who.
"This was all before we joined the EU. We were just kids but we were filling stadiums all round the world. Britain was the centre of the world. You got that because Britain was doing its own thing. It was independent. Not sure we'll ever get that against when we're ruled by bureaucrats in the European Union."
• Sir Michael Caine – The actor has said he is a reluctant Leaver. He said: "I don't know what to vote for. Both are scary. To me, you've now got in Europe a sort of government-by-proxy of everybody, who has now got carried away. Unless there is some extremely significant changes, we should get out."
• Elizabeth Hurley – The actress said: “If it means we can go back to using decent lightbulbs and choose high-powered hairdryers and vacuum cleaners if we so wish, I'm joining Brexit for sure.”
• Sol Campbell – The former England international football star said he is backing Brexit so that young British sporting talent would be nurtured and given greater opportunities at British clubs. He said: "I'm looking at the sporting side - how youngsters aren't getting the opportunities at some of the big clubs and some of the big clubs are bringing in youngsters from 14, 15, 16 and becoming home-grown, which is pushing some of our youngsters out."
Other sportspeople supporting Leave are cricketer Sir Ian Botham, former England goalkeeper David James, racing driver Perry McCarthy, and Olympic rower James Cracknell.
Follow all the live updates on the Put it to the People protest here
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