The headline figure marked a public victory for Make Poverty History.
But campaign groups criticised the deal as a compromise, pointing out Mr Blair had failed in his demand for the money to kick in straight away. It will become available from 2010.
The richest countries in the world give about $50bn a year in aid. Mr Blair wanted to double that from next year but his plans were delayed by four years.
Aid groups claimed some of the increases had been agreed previously. ActionAid's policy head Charles Abugre said: "This will not make poverty history."
In its communiqué, the G8 sent a strong message to the rest of the world to strike a deal to make trade fairer for poor countries, announced universal treatment for Aids victims and confirmed plans to cancel billions of pounds of debts.
The Prime Minister said of the aid package: "It is a beginning, not an end.
"We came here in solidarity with the continent of Africa and we have come here to announce a plan for action in partnership with Africa. It is not the end of poverty in Africa but it is the hope it can be ended."
He acknowledged many of the campaign groups and the millions who participated in the Live8 events would be disappointed. "It isn't all everyone wanted but it is progress, real and achievable progress," he said. "It is the definitive expression of our collective will to act in the face of death and disease and conflict.
"We do not, simply by this communiqué, make poverty history. But we do show it can be done and we do signify the political will to do it."
He paid tribute to the campaign led most publicly by rock stars Bono and Sir Bob Geldof. "This was a quite remarkable campaign ... that has been led with a great deal of dignity and an enormous compassion and decency."
The Nigerian President Olusegun Obasanjo, called the G8 summit's achievements a "great success". But Mark Malloch-Brown, the chief of staff to United Nations secretary general Kofi Annan, said: "There will be a lot of smokescreen and buckets of G8 paint thrown over old aid."
Jo Leadbetter, head of advocacy at Oxfam, said; "If the $50bn increase had kicked in immediately, it could have lifted 300 million out of poverty in the next five years."
War on Want said the G8 had given less than a tenth of its demands on debt cancellation and not even a fifth of what it called for on aid.
It said just $15bn of the $50bn was new money. "This is far too little, far too late," said John Hilary, its director of campaigns.
The main setback for the UK was its failure to get the US to endorse its plan for a financial device known as the international financial facility - under which governments would borrow money from the financial markets and deliver it straight to the frontline.
Britain also failed in its drive to get the G8 to pledge to eliminate its subsidies for exported food by a specific date, instead calling on negotiators to set a date at a meeting of the World Trade Organisation in December.
* Mr Blair said the G8 had agreed to aid amounting to $3bn over the next few years to help build peace in Israel and Palestine.