Dr Rowan Williams, spiritual head of the world's 78 million Anglicans, today called on wealthy governments to fulfil their promises on aid, trade and development or see the world's poor continue to suffer disease, starvation and death.
The call came at the end of a procession of 1,000 faith leaders and bishops from central London to Lambeth Palace.
The archbishop said that there was a "genuine opportunity" to halve poverty by 2015 - the slogan on the placards distributed throughout the march, which was headed by a banner proclaiming "Keep the promise".
Prime Minister Gordon Brown also spoke, lavishly describing the march as "the greatest public demonstration of faith that this great city has ever seen."
"A hundred years is too long to wait for justice and that is why we must act now". You have sent a symbol, a very clear message with rising force that poverty can be eradicated, poverty must be eradicated and if we all work together for change poverty will be eradicated," he added.
Mr Brown joined Dr Williams in warning that time was running out if the United Nations Millennium Development goals were to be achieved.
In a letter to 10 Downing Street, the archbishop declared: "In our human family the continuing consequence of failure is the death of millions of women and children from childbirth and preventable childhood diseases."
It continued: "Millions more have hopes for sustainable life diminished because of poverty-fuelled conflict, lack of education and gender inequality, all of which undermine a new generation's liberation from HIV."
Other faith leaders on the march were Cardinal Cormac Murphy-O'Connor, leader of Catholics in England and Wales; Sir Jonathan Sacks, chief rabbi of the United Hebrew Congregations of the Commonwealth; the former secretary general of the Muslim Council of Britain Sir Iqbal Sacranie, and Network of Sikh Organisations director Dr Indarjit Singh.