Manmohan Singh served as the country's prime minister from 2004 to 2014.
Former Prime Minister Manmohan Singh turns 86 today. On his birthday, Prime Minister Narendra Modi, Congress president Rahul Gandhi and other leaders greeted him on Wednesday.
Prime Minister Narendra Modi greeted his predecessor on Twitter and prayed for his long life.
"Greetings to our former prime minister Dr Manmohan Singh ji on his birthday. I pray for Dr Singh's long life and good health," PM Modi tweeted.
Congress president Rahul Gandhi praised Mr Singh's selfless service to the nation.
"Manmohan Singh ji's birthday is an opportunity for us to appreciate and remember his many years of selfless service and dedication to the cause of nation building. I wish him a very happy birthday and good health and happiness always," Rahul Gandhi said on Twitter.
Delhi Chief Minister Arvind Kejriwal called Mr Singh a man of integrity, sobriety and humble nature.
"I wish a very happy 86th birthday to Dr Manmohan Singh, our former Prime Minister. A man of integrity, sobriety and humble nature. I pray for his long & healthy life," Mr Kejriwal tweeted.
Home Minister Rajnath Singh, Madhya Pradesh Chief Minister Shivraj Singh Chouhan, Dravida Munnetra Kazhagam president MK Stalin, Punjab Chief Minister Amarinder Singh and Bengal Chief Minister Mamata Banerjee also tweeted best wishes on Manmohan Singh birthday.
Former Prime Minister Manmohan Singh was born in Gag, now in Pakistan, on September 26, 1932. Mr Singh is an economist who became a politician and was the country's prime minister from 2004 to 2014.
Manmohan Singh, who was the first Sikh in office, was also the first prime minister since Jawaharlal Nehru to be re-elected after completing a full five-year term. Mr Singh's political career began in 1991 when he was appointed as the country's Finance Minister under the leadership of late prime minister PV Narasimha Rao. It was the same year during which he helped usher in "liberalisation and privatisation" to the Indian economy.