Joseph was born in 1948 in Hong Kong. He is a graduate in Economics and Statistics of the University of Hong Kong (1970). He joined the Civil Service in 1971 as a Statistician. In 1976 he was transferred to the Economic Services Branch, working closely with the Financial Secretary and the Secretary for Economic Services on budgetary matters and on economic analysis.
In 1982, he was transferred to the Monetary Affairs Branch as a Principal Assistant Secretary. In 1985, he was appointed Deputy Secretary for Monetary Affairs. In February 1991, he was appointed Director of the Office of the Exchange Fund. Mr. Yam was instrumental in the establishment of the Hong Kong Monetary Authority which was set up in April 1993. He is its first Chief Executive.