Upon returning to India, he became heavily involved in the labour movement, becoming general secretary and then president of the All-India Railwaymen's Federation and twice serving as president of the All-India Trade Union Congress. Giri first entered politics in 1937 when he became minister of labour and industries for the Congress Party government formed in the Madras Presidency. When the Congress governments resigned in 1942, he returned to the labour movement as part of the "quit India" movement and was imprisoned by the British.After India gained independence, he was first appointed high commissioner to Ceylon and then successfully ran for parliament in 1952, serving as minister of labour until resigning in 1954. Over the next decade, he served as governor, a largely ceremonial position, of Uttar Pradesh, Kerala, and Mysore, before being elected vice president of India in 1967. Giri became acting president of India in 1969 upon the death in office of Zakir Hussain and decided to run for that position in the ensuing election. The Congress Party led by Indira Gandhi chose to support Neelam Sanjiva Reddy for the position, but he was able to prevail anyway (reportedly due to a last-minute change in the decision by Indira Gandhi), serving until 1974. He received India's highest civilian decoration, the Bharat Ratna, in 1975.