Scams that surfaced during UPA II may have undone the good work of the 81-year-old leader, who had achieved the distinction of serving two tenures as Prime Minister, the longest after the first PM Jawaharlal Nehru's 17 years in office.
After tomorrow's counting of votes in the Lok Sabha elections in which the UPA is projected by exit polls to suffer a defeat, Singh will tender his resignation on Saturday.
A celebrated economist, he entered politics at the height of the 1991 economic crisis when late Prime Minister P V Narasimha Rao inducted him into the government as Finance Minister.
Together they lifted the economy out of the balance of payments crisis and then paved the way for the economic reforms on which no successive government has looked back.
A technocrat who had occupied various positions including as Reserve Bank Governor and Secretary General of the South-South Commission, he had earned a name for probity and integrity that made him the automatic choice for Sonia Gandhi when she decided to renounced the post of Prime Minister.
Taking over as Prime Minister from the NDA government in the aftermath of the 2002 post-Godhra riots and a surcharged communal atmosphere, Singh's administration brought in a sense of balance in the situation.
Notwithstanding pulls and pressures from allies, especially the Left parties, Singh displayed considerable determination to go ahead with the Indo-US nuclear deal and to end the sanctions regime against India even unmindful of the threats to his government.
A renowned economist, his governments also delivered a robust 8.5 per cent GDP growth for most of his tenure but the scams--2G, CWG and Coal block allocations--and the resultant policy paralysis of the government stymied his performance.
UPA II could never come out of the rut, a point the corporates initially and the BJP PM candidate Narendra Modi exploited to the hilt to attack the government. Ironically, a man whose personal honesty has never been questioned came to preside over a government that was marked by a series of scams.
The perceived dual power centre in the Congress in the form of power vesting with party chief Sonia Gandhi also came to haunt him with critics attacking him as the weakest Prime Minister the country has had.
Books by his former media adviser Sanjaya Baru and some other bureaucrats have only helped to highlight such a charge.
However, Singh has maintained that history will be kinder to him than the current assessments.
Singh's rise to the top highlights what a man with a humble background can achieve in Indian democracy.
He was the first Sikh to become the Prime Minister after an Italian Christian--Sonia Gandhi--nominated him to the post to which he was sworn in by a Muslim President A P J Abdul Kalam.
Born on September 26, 1932 in Gah village of Pakistan's Punjab province, Singh held several key positions like Economic Adviser to the government and Deputy Chairman of Planning Commission before being catapulted to the position of the Prime Minister in 2004.
When Congress was in a position to form government at the Centre after the 2004 Lok Sabha polls with the help of several other parties, nobody expected Singh to become the Prime Minister as the party chief was the natural claimant for the post.
However, Gandhi threw a surprise at the last minute by proposing the name of Singh for Prime Ministership which was reluctantly endorsed by the party members.
He went on to head the Congress-led United Progressive Alliance (UPA) government as the 14th Prime Minister and its success probably made Sonia Gandhi to give him another term starting 2009.
His first five-year tenure was marked by major initiatives like MNREGA and RTI. The highlight of that term was also the strong stand that the normally soft-spoken Singh took on the Indo-US civil nuclear deal in the face of strong opposition by the Left parties, which were then part of his government.
Putting his foot down on the issue, Singh asserted that he will not go back on the international commitment even if it means the fall of his government.
Left parties did withdraw support to his government but it survived in the confidence vote with the help of Samajwadi Party and BSP.
Besides working for stronger ties with the US, Singh's personal commitment to maintaining peaceful ties with Pakistan helped keep bilateral relations on track.
Singh's second term was tainted with three major scams whose combined amount was said to be to the tune of whopping Rs four lakh crore approximately, prompting the opposition to allege that there was "unprecedented" corruption.
Adding to the woes of his government was Anna Hazare-led anti-corruption crusade that acquired widespread dimensions at the cost of Congress.
As predictions of bad performance by Congress came, party leaders started saying that the government did not communicate well its achievements which is seen as a veiled attack on Singh for remaining silent while attacks took place.
In his political career, Singh has been a Member of Rajya Sabha since 1991.
During the NDA rule of Atal Bihari Vajpayee between 1998 and 2004, Singh was the Leader of the Opposition in the Rajya Sabha.
Earlier, he joined the Government of India as Economic Advisor in the Commerce Ministry in 1971. This was soon followed by his appointment as Chief Economic Advisor in the Ministry of Finance in 1972.
Among the many governmental positions that Singh has occupied are Secretary in the Ministry of Finance, Governor of the Reserve Bank of India, Advisor to the Prime Minister and Chairman of the University Grants Commission.
Among the many awards and honours conferred upon Singh in his public career, the most prominent are the Padma Vibhushan (1987); the Jawaharlal Nehru Birth Centenary Award of Indian Science Congress (1995); the Asia Money Award for Finance Minister of the Year (1993 and 1994); the Euro Money Award for Finance Minister of the Year (1993), the Adam Smith Prize of the University of Cambridge (1956); and the Wright's Prize for Distinguished Performance at St. John's College in Cambridge (1955).
He is a recipient of honorary degrees from many universities including the Universities of Cambridge and Oxford. His initial education took place in Pakistan's Punjab province.