But Singh did not escape unscathed from Tuesday's closely fought confidence vote, with a bribery scandal threatening his squeaky clean image.

He admitted he was ‘extremely sad’ after Opposition MPs accused his government of bribing them to abstain.

"He was challenged, he was abused, all sorts of things were said, but he has come out victorious," said B G Verghese, author and commentator. "It is a great moral, political victory."

Manmohan Singh's reputation was forged in his time as Finance Minister in the 1990s, when he pushed through a series of economic reforms which set the stage for India's subsequent boom and entry onto the world stage as a rising economic power.

But he seemed an unlikely choice for Prime Minister, thrust into the limelight only because Sonia Gandhi turned down the top job after winning elections in 2004.

Time and again, Manmohan Singh seemed dwarfed by Sonia Gandhi and ill-suited to the rough and tumble of Indian politics. He seemed to reach a nadir in 2007 when his Left allies forced him to back down over the nuclear deal.

Manmohan Singh had staked much of his prestige on the deal, shaking hands with US President George W Bush on first announcing it at the White House in 2005.

He was visibly crestfallen when forced to back down in 2007, as his Cabinet colleagues were not prepared to face early elections.

But Manmohan Singh, 75, appeared to find a second wind, and finally ended up getting the Congress party on-side. The government pushed ahead with the deal, and the Leftists withdrew, paving the way for Tuesday's vote.

He is India's first PM to hold a doctorate, famous for his spartan lifestyle and bookish manner.

Grey-bearded and bespectacled, Singh dresses in homespun white long tunic-pyjamas and a trademark sky-blue turban. Lunch and dinner are two rotis -- a flat Indian bread -- and lentils.

Born into a poor Sikh family in Pakistan, Manmohan Singh won scholarships to Cambridge and Oxford, earning a doctorate with a thesis on the critical role of exports and free trade in India's economy.

But he has never won an election and sits in the mostly nominated Upper House of Parliament.

Critics say his career, including as UN civil servant and government bureaucrat, underline a life where advancement has carried more weight than pursuing strong political ideals.

People who have known and worked with Singh for more than a decade describe him as a quiet, hardworking man and a deep thinker who shuns the perks and corruption that many Indian politicians thrive on.

"He's very honest, sincere and hardworking, the kind you will hardly find now," said D H Pai Panandikar, the head of a private economic think-tank and Manmohan Singh's Cambridge classmate.

"He cannot dominate and say something loudly like 'get this done'. He's not tough-talking. It's a handicap."

Manmohan Singh doesn't deny he is a politician by accident.

"The greatness of democracy is that we are all birds of passage," he said in his concluding speech during the debate on the confidence vote.

"We are here today, gone tomorrow. But in the brief time that the people entrust us with this responsibility it is our duty to be honest and sincere in the discharge of these responsibilities."

Since coming to the job in 2004, Manmohan Singh has worked 14-hour days, devouring files and coming to grips with the complexities of running a hugely diverse country of one billion people.