US President Barack Obama played down differences at the summit, declaring it a "turning point" for the world economy.
"We have agreed on a series of unprecedented steps to restore growth and prevent a crisis like this from happening again," Obama told a news conference.
"We've also rejected the protectionism that could deepen this crisis."
Analysts described the G20's decisions as more far-reaching than expected. All parties got at least a slice of what they were expecting, and they all hailed the creation of a "new world order."
Developing countries received $1.1 trillion of additional resources for the world economy, which will be allocated through the International Monetary Fund and other institutions.
Germany and France celebrated a call for strengthened regulation and supervision, as well as the establishment of a regulatory watchdog (the new Financial Stability Board).
And the US welcomed a decision to end the era of banking secrecy and take action against non-cooperative jurisdiction, including tax havens.
As a result, stocks rallied: the index of top European shares was up 5%, while on Wall Street, the Dow Jones was up 3.3 percent. But economists cautioned against euphoria, as new data are expected to be released this week.
"Today's agreement begins to crack down on the cowboys in financial markets that have brought global markets undone," Australian Prime Minister Kevin Rudd said.
UK Prime Minister Gordon Brown, the summit's host, said governments had committed $5 trillion to public stimulus of the economy this year and next, before even taking into account the extra commitments from the summit in London.
He did not say how that squared with the stimulus estimate he gave just a day earlier - of about half that amount.
Help for developing countries
The $1.1 trillion that would be made available to help the world economy includes $250 billion of IMF reserve units called 'Special Drawing Rights'.
In addition, the IMF would see its own resources tripled, with up to $500 billion of new funds, of which $40 billion would come from China. Much of that is likely to go to struggling poorer countries, notably in eastern Europe.
The summit also agreed a trade finance package worth $250 billion over two years to support global trade flows, which have shrunk under the impact of the credit crunch: a boost for the world's major exporters.
Tightened financial regulation
Major failures in the financial sector called for a major overhaul of regulatory and supervision systems. G20 leaders agreed to create a new Financial Stability Board to replace the current Financial Stability Forum. Although the board will have a "strengthened mandate" to oversee the world financial system, it will not have specific control over financial companies.
The summit also agreed to extend regulation and oversight to all systemically-important financial institutions, instruments and markets, including the largest hedge funds.
New rules will be drawn up regarding banks' capital requirements and credit-rating agencies once the crisis is over.
To "take action" against tax havens and other non-cooperative jurisdictions, including the threat of sanctions if necessary, the Organisation for Economic Co-operation and Development published a list of such uncooperative countries, the most culpable of which were Costa Rica, Malaysia, the Philippines and Uruguay.
G20 to be continued
Leaders at the G20 agreed to meet again before the end of the year to evaluate progress on the agreed action plan.
Some announced that the next meeting would take place in the autumn in Japan. But Mr Sarkozy announced with equal certainty that the follow-up would be in New York in September.
If the next summit were to be held in New York, it would coincide with the opening of the UN general assembly, so most world leaders would already be in town.
(EurActiv with agencies.)
