"Birthday greetings to former PM Dr Manmohan Singh Ji. Praying for his long and healthy life," tweeted PM Modi.
Congress leader Rahul Gandhi also wished Dr Singh on his birthday. "Wishing one of India's finest statesmen, Dr Manmohan Singh ji a very happy birthday. His humility, dedication and contribution to India's development, have few parallels. He is an inspiration to me, and to crores of other Indians. I pray for his good health and happiness," tweeted the Wayanad MP.
Singh was born on September 26, 1932, in Punjab's village of Gah before the partition. He studied at Punjab University, Cambridge, and Oxford.
Dr Singh, who was the Prime Minister for two consecutive terms (from 2004-2014) has turned 90 today. He is a renowned economist, credited for introducing sweeping reforms in the 1990s.