BJP leader Swapan Dasgupta and three others took oath as members of the upper house in the presence of Vice President Venkaiah Naidu on Tuesday.
Besides Mr Dasgupta, senior advocate Mahesh Jethmalani, journalist John Brittas and CPI(M) leader V Sivadasan also took oath.
Mr Brittas and Mr Sivadasan are newly elected members whereas Mr Jethmalani is nominated and Mr Dasgupta is a re-nominated member of the Rajya Sabha.
On his re-nomination to Rajya Sabha, Swapan Dasgupta on Wednesday had said that he plans to use his term to highlight issues of West Bengal and to focus on the educational system in the country.
"I am grateful to President for nominating me again to the Rajya Sabha. I hope to use the remainder of my term to raise and highlight issues which primarily concern the state of West Bengal and also to explore some of the issues which are concerned with problems and prospects of education in India," Mr Dasgupta had told ANI.
Mr Dasgupta had tendered his resignation as a Rajya Sabha MP and fought the West Bengal Assembly election. However, he lost the polls.