The prime minister said the unanimous decision by the International Atomic Energy Agency (IAEA) was a "milestone" in India's cooperation with the international community in the peaceful use of nuclear power.
"The civil nuclear initiative is good for India and good for the world," Singh said in a statement after arriving in Sri Lanka on the eve of a South Asian summit.
"As we move forward towards our goal of sustainable development and energy security, the peaceful uses of atomic energy will play an increasingly important role," said Singh.
Singh put his Congress-led coalition government on the line to push through the deal in the face of strong opposition from left-wing parties which said the accord threatened India's military strategic programme and would lead to US interference in foreign policy.
The government survived a hard-fought confidence vote in parliament sparked by the political left's opposition to the pact.
The so-called safeguards agreement will subject Indian nuclear facilities to IAEA supervision and is a pre-condition to the US-India deal under which Washington will supply New Delhi with civilian nuclear fuel and technology.
Energy-hungry India, which needs new sources of power to expand its fast-growing economy, still needs a waiver from the Nuclear Suppliers Group (NSG) -- 45 states exporting nuclear fuel and technology -- and ratification by the US Congress before the deal can go through.
The NSG was expected to hold its next meeting on August 21.
"One big step has been taken today ... the NSG would the next big step," foreign secretary Shiv Shankar Menon told reporters.
"We have been talking to NSG countries" for a clean exemption that "will enable us to resume full civil nuclear cooperation with the rest of the world," he said.
The IAEA approval followed an intensive diplomatic offensive by India, which last month sent envoys around the world to lobby for the final international clearances.
New Delhi would now bring all its weight to bear to get the deal through the NSG, officials said.