He is currently the chairman of the review committee set up under Fiscal Responsibility and Budget Management Act, 2003, under the purview of Ministry of Finance, Government of India.

Following that, he has held the following positions: As Revenue Secretary (July 1996 – August 1998), he oversaw the Dream Budget (1997–98), one of the most ambitious tax reforms so far.

[9] Similarly, corporate tax rates were also significantly reduced apart from simplifying and merging the widely varying customs and excise duty structure.

[17] Comprising the Golden Quadrilateral and the North-South and East-West corridors, it was one of the flagship scheme of the Indian Government and NHAI (National Highway Authority of India).

Singh has authored The New Bihar which is a collection of essays on the state's model of development, shedding light on its achievements, shortcomings, and the challenges ahead.

His other publication, "Not by Reason Alone", is a commentary on Indian political economy, analysing the various reforms pertaining to infrastructure, finance, government policies and Centre-state relations.

On 29 April 2016, NK Singh was conferred with the 2nd class Gold and Silver of the Order of the Rising sun by the Japanese Government.

In the recorded conversations in the Nira Radia tapes, NK Singh[24] is heard stating that he got the order of the speakers in the Rajya Sabha changed to give an edge on retroactive tax rebates to Reliance Industries.