"The appointment is in accordance with the rules and based on the powers of the government. There are several precedents to this," he told PTI.
Accusing BJP of politicising the issue, he said the main opposition party would be given a "fitting reply" in Parliament if it raised the matter.
Ramasundram's appointment has seen government and Central Vigilance Commission (CVC) lock horns over considering an officer whose track record was under question.
Government also went by the opinion of Solicitor General Mohan Parasaran in picking Ramasundaram when he opined that it had "sufficient discretion to reject" if a single name is recommended.