Broadbent joined 2,000 anti poverty campaigners in the pouring rain for a concert in Belfast's Botanic Gardens, where he recited a poem to the crowd.
He said: "With so many people turning out, even on a day like today, it shows there is an enormous will to get people to listen to the issues and to correct what is clearly not right. Many people are not happy with the situation.
"There is enough food to go around but it is not getting to one in eight people. It is very, very serious. I would like them (world leaders) to redress some of the tax issues where the biggest companies are not paying the tax that they should be and how the aid is distributed."
The Big IF event was organised by a range of charities including Oxfam, Trocaire and the Enough Food For Everyone If campaign.
Tanzanian teenager Frank Kadeta, 16 - who almost starved to death after drought hit his home village when he was a child, spoke out. "Sometimes I was so weak it was painful because of hunger. It affected my life," said the Save the Children ambassador. "I want to tell world leaders to stop the hunger because many children and people die every day."
The Ulster Orchestra opened the gig - which included performances from Britain's Got Talent finalist Jordan O'Keefe, actor Richard Dormer, Duke Special and General Fiasco. But a silence fell over the crowd as Broadbent took to the stage and performed Seamus Heaney's poem on Ireland's Great Famine, For the Commander of The Eliza.
Marian Martin, 64, and her 25-year-old daughter Fiona travelled from Glasgow just for the concert, spending just fours in the city before making the journey home by ferry. Mrs Martin, a social justice campaigner, said she feels so strongly about world hunger she had to make the event.
"We feel we have to put pressure on governments to act, especially in regard to the tax dodging going on," she said. "We have to have clearer tax legislation and we have got to stop land grabbing."
Melanie Holmes, 36, from Belfast, said she hopes more people would have come to the event,
"I came here to be part of the movement and say to the G8 leaders something needs to be done for people," she said.
"It's an opportunity for my family to show what we believe in."
Indie group Two Door Cinema Club, who headlined the concert, said millions of lives could be saved if people with some sway tackled injustices around the world.
Frontman Alex Trimble said the group has seen real poverty on the road, particularly in Africa and South America.
"The solution is so simple and the best thing about the IF campaign is that it puts it so simply," he said.
"That was the main thing that attracted us."
He said the campaign's four points are to get governments to provide more aid, to stop big companies avoiding tax, stopping farmers being forced off their land and getting governments to be honest with their people.
"Those are four things that can be easily addressed, there's money that can go into these things to make them happen," he added.
"If we do that then there'll millions and millions of people who don't die from starvation."
Lead guitarist Sam Halliday said the cause is not about asking people to put £10 in a pot.
"It's much greater than that and it's not solved by the generosity of a relatively low amount of people," he added.
"It's down to people who have sway over what to us is a lot of money. It's pocket change to a government."
From the web
COMMENT RULES: Comments that are judged to be defamatory, abusive or in bad taste are not acceptable and contributors who consistently fall below certain criteria will be permanently blacklisted. The moderator will not enter into debate with individual contributors and the moderator’s decision is final. It is Belfast Telegraph policy to close comments on court cases, tribunals and active legal investigations. We may also close comments on articles which are being targeted for abuse. Problems with commenting? email@example.com