Mrs Lau joined the Administrative Service of the Hong Kong Government in October 1976. Since then, she has served in various bureaux and departments, holding such senior positions as Deputy Secretary (Information Technology and Broadcasting), Director of Urban Services and Director of Food and Environmental Hygiene. She was Permanent Secretary for the Environment, Transport and Works (Environment and Transport) from July 2002 to January 2004, and Permanent Secretary for Housing, Planning and Lands (Planning and Lands) from May 2004 to June 2007.

Mrs Lau assumed the post of Permanent Secretary for Commerce and Economic Development (Communications and Technology) in July 2007 and was appointed as the Secretary for Commerce and Economic Development on 12 July 2008. Her policy responsibilities include external commercial relations, inward investment promotion, intellectual property protection, industry and business support, tourism development, consumer protection, competition, development of information technology, telecommunications, broadcasting, film and creative industry, and innovation and technology.