Veteran diplomat and former Foreign Secretary Shivshankar Menon on Saturday took over as National Security Adviser.
60-year-old Menon, who will serve in the rank of Minister of State till further orders, took charge from M K Narayanan, who has been appointed as West Bengal Governor.
The 1972-batch IFS officer, who retired as Foreign Secretary in July last year, brings with him vast experience in diplomacy.
A highlight of his diplomatic career was the key role he played in negotiations for the landmark Indo-US civil nuclear deal that ended India's long isolation in the atomic sector.
After being named as the NSA on Thursday, Menon said he was "very conscious that it is a big responsibility and I will do my best."
Earlier this morning, Prime Minister Manmohan Singh hosted a farewell lunch for Narayanan, where Finance Minister Pranab Mukherjee, Home Minister P Chidambaram, Defence Minister A K Antony and MoS in PMO Prithviraj Chavan were present.
Singh hailed Narayanan as "one of the finest" civil servants.
He particularly referred to Narayanan's contribution to negotiations on the Indo-US nuclear deal and said it would not have come through without his role.
"His best is yet to come. He is going to Raj Bhavan, which is public service," Singh said.
Narayanan will take over as West Bengal Governor on Sunday.