Mr Sen was India’s ambassador to the United States from 2004 to 2009. He was also India’s ambassador to Mexico (1991-92), to Russia (1992-98), and Germany (1998-2002), and served as High Commissioner to the United Kingdom (2002-04). From 1986 to 1991, he was foreign and defence policy advisor to successive prime ministers and had several assignments as special envoy of the prime minister for meetings with heads of state or government.
Mr Sen joined the Indian Foreign Service (IFS) in 1966. Between 1968 and 1985, he served in Indian missions in the former USSR, the United States and Bangladesh. He also served as deputy secretary, Department of Atomic Energy (DAE) and secretary to the Atomic Energy Commission, and as deputy secretary and joint secretary in the Ministry of External Affairs. He has participated in around 180 bilateral and multilateral summit meetings in six continents.
Mr Sen has also served on the board of Tata Motors as a non-executive independent director from 2010 to 2012.