Tens of thousands of people have gathered in Hyde Park for an anti-hunger demonstration, hosted by lobby group Enough Food For Everyone If.
High profile actors, football champions and film directors have all spoken at the rally with Danny Boyle insisting that ending world hunger would be "the greatest gold medal Britain could win in 2013".
The film director called on world leaders to "fight and fight and fight" to stop people dying through lack of food.
Boyle made the comments at a protest rally as David Cameron hosted a Nutrition Summit in London.
Hosting a conference intended to drum up billions of dollars for the developing world, the Prime Minister backed a target of saving 20million children from chronic malnutrition by 2020.
The government has committed to giving an extra £375 million to help feed the world's poorest children.
Separately, Boyle told the crowd: "I'd like to reflect for a moment on the Olympics, on the opening ceremony on which I worked.
"It completely horrifies me, when I think about that wonderful procession of optimistic, enthusiastic athletes with their flags of their countries - that in the countries represented by those flags more than three million children die of hunger every year."
He went on: "Anyone who says that we can't crack the hunger crisis is wrong.
"This is my dream - it's a passionate dream - that in Olympics to come there will be no-one dying of hunger in any of the countries whose wonderful flags wave in the wind. And it is a fight that will be won.
"We expect our government and other world leaders to fight with all the energy and cunning and determination of Chris Hoy and Mo Farah and Jessica Ennis and Bradley Wiggins - to fight and fight and fight to end hunger until they win."
The rally marked 10 days until Mr Cameron takes charge of the G8 meeting in Northern Ireland.
The campaign said there were three key summits, including today's, leading up to the meeting which could tackle the causes of hunger.
There was a so-called visual petition of 250,000 spinning flowers, featuring two million petals to represent the children who die because of malnutrition each year.
Microsoft billionaire Bill Gates praised the UK for "leading the way" on tackling hunger.
Mr Gates said: "The UK is keeping its promise to the world's poor, largely because all of you remind your leaders regularly, and loudly, that this stuff matters. Now is our chance to make a significant difference."
Alongside the headline speakers, former Archbishop of Canterbury Rowan Williams and actor David Harewood also appeared.
Dr Williams led a minute's silence "to reflect on the pain" of death by malnutrition.
He said: "Thinking about these unnecessary deaths, there should also be righteous anger. Fury that the injustice of hunger has gone on too long. And so at the end of our silence, we must make a huge noise, to signify that we will never be silent on the things that matter."
Homeland star Harewood insisted that "there can be enough food for everyone".
He said: "We've already changed the diaries of the G8 leaders, we've already changed their agenda. Now we just need to remind them they need to change the world.
"That's why we need all of you to speak up today."
The crowd was also played a video message from former England captain David Beckham.
After the Government committed to giving an extra £375 million to help feed the world's poorest children, Beckham said:
"We've had good news. Earlier today the Prime Minister met with other world leaders and has made a real commitment to ending child malnutrition and hunger.
"There is more to do though and you can help."
Organisers said around 45,000 people attended the event.