Ng graduated from the University of Hong Kong in 1970 with a Bachelor of Social Science (BSocSc) and joined the Hong Kong government in June 1970. He served briefly as an Assignment Officer and then as an Executive Officer II before transferring to the Administrative Service in August 1971. He was Deputy Secretary for the Civil Service from November 1985 to February 1987, Deputy Secretary for Trade and Industry from February to July 1987, Deputy Director of the Information Services Department from July 1987 to March 1989, Secretary-General of the Standing Commission on Civil Service Salaries and Conditions of Service from May 1989 to May 1991 and Director of Administration from June 1991 to January 1994.
He rose to be Director of Bureau in January 1994 when he was appointed Secretary for Constitutional Affairs, which office he held until August 1997 when he was appointed Secretary for Transport, a role he held until April 2002. He retired from the government in July 2003. In 2005, he was appointed chairman of the Public Service Commission, where he stayed until his retirement in April 2014.
- "Retirement of Mr Nicholas Ng and Mr Dominic Wong". Hong Kong Government.
| Secretary for Constitutional Affairs
| Secretary for Transport
as Secretary for the Environment, Transport and Works