He started his career in the Civil Service in the Security and Intelligence Division, Ministry of Defence, in 1970 after graduating with a Bachelor of Arts degree in Philosophy, Politics and Economics from Oxford University on a President's Scholarship.

He obtained a Master of Science in International Relations from the University of London, United Kingdom in 1974.

Mr Teo rose rapidly in the Intelligence Service to become the Director of the Security and Intelligence Division in 1979, and concurrently held the position of Director, Internal Security Department in the Ministry of Home Affairs from 1982 to 1986.

He was appointed Permanent Secretary (Defence) in 1994. In 1998, he was appointed Permanent Secretary (Prime Minister's Office) and concurrently held the post of Permanent Secretary (Defence) until 2000. He retired from the Administrative Service in 2005 after 35 years of distinguished service in the Singapore Civil Service.

Mr Teo had also served as Director on various government-linked companies over the years, including those related to the defence industry.

He was Chairman of Singapore Technologies Pte Ltd from 1995 to 2000 and ST Kinetics from 2001 to 2004. He was also Chairman of the Health Corporation of Singapore Pte Ltd from 1996 to 1998 and the Civil Service College from 2001 to 2005.

For his contributions to the Singapore Public Service, Mr Teo was awarded the Public Administration Medal (Gold) in 1983, the Meritorious Service Medal in 1997 and the Distinguished Service Order in 2006.