Campaigners representing church groups and NGOs will urge Brown on Monday to call time on the global greed they say is behind the worst financial crisis in history.
Protesters are planning to gather outside the Guildhall with alarm clocks and banners reading "Call Time on Global Greed" as Prime Minister Gordon Brown addresses representatives of the financial sector at the Lord Mayor of London's banquet on Monday night.
Groups involved in the protest include the Trade Justice Movement, ActionAid, Catholic development charity CAFOD, the Jubilee Debt Campaign coalition of NGOs and church groups, and War on Want.
The campaigners are angry that billions of dollars of taxpayers' money have been spent on rescuing troubled banks and financial institutions while "the world's poorest people remain saddled with an unfair economic system and have received nothing," a spokesperson for the groups said.
They are calling for a fundamental reform of the current economic system.
Benedict Southworth, chair of the Trade Justice Movement, commented: "The past few months have seen one of the most significant financial crises in North American and European history, a crisis caused by global greed - a reckless and unregulated economic system which has been biased against the poor for decades.
"It's time for a radically different system which reduces inequality, creates jobs and puts people before profit, within a low carbon economy. It's essential that rich countries do not use this crisis as an excuse not to make deep cuts in carbon emissions and agree a post 2012 climate change deal. Instead we need to grasp this as an opportunity to set the world economy on the path to sustainability."
The protest comes just days before leaders of the world's richest economies gather in Washington, D.C., on Saturday for the G20 summit to discuss the financial crisis.
The protesters are calling for a democratic forum that allows poor countries to be involved in decisions concerning global economic reforms.
"The financial crisis has graphically demonstrated to people in rich countries what the poor have known for years, that the current international economic system doesn't work," said Meredith Alexander, Head of Trade and Corporates at ActionAid.
"We need a radically different economic system which puts people first. Most importantly, the world's poorest people must have a full and equal say in developing this system. Decisions must not be taken by organizations that only represent rich countries."