Traditionally, it is Asia's turn to lead the UN under the rotating system, although some Eastern European nations and even the US have been talking about pitting their candidate, despite an unwritten rule which prohibits the top man coming from one of the five permanent members of the UN Security Council.
Among the Asian contenders, Jayantha Dhanapala, the adviser to Sri Lanka's president and a former UN under secretary general, is considered the front-runner.
Foreign Policy magazine also named South Korea's Minister of Foreign Affairs and Trade Ban Ki Moon, Thailand's Deputy Prime Minister and former foreign minister Surakiart Sathirathai, Kemal Dervis of Turkey, who heads the UN Development Programme, former Poland president Aleksander Kwasniewski, and Latvian Vaira Vike-Freiberga as other contenders for the job.
Though the secretary general is finally elected by the UN General Assembly, the UN Security Council must agree to the name before the General Assembly votes.
Indian government sources said a formal announcement of its endorsement of Dr Tharoor's candidature is likely in a "day or two."
Mumbai-born Dr Tharoor, who turned 50 in March, did his schooling in Mumbai and Kolkata, before going to St Stephen's college in Delhi. A contemporary of director Mira Nair and actress Lillette Dubey at university, he is considered one of the brightest members of his generation, getting a PhD from the Fletcher School of International Diplomacy at Tufts University in the USA when he was in his early 20s.
He is also an accomplished writer, has written novels, books of history and recently published a biography of Jawaharlal Nehru.