Dr Tan currently serves as a Special Advisor to the Government of Singapore Investment Corporation Private Limited (GIC), and was previously the seventh President of the Republic of Singapore from 1 September 2011 for a six year term.

Dr Tan was elected as a Member of Parliament in 1979 and was appointed Senior Minister of State in the Ministry of Education. From October 1983 to January 1985, Dr Tan served as the Minister for Finance and concurrently as the Minister for Trade and Industry. From January 1985 to December 1991, he served as the Minister for Education.

In December 1991, Dr Tan stepped down from the Cabinet to return to the private sector as Chairman and Chief Executive Officer of OCBC. Dr Tan rejoined the Cabinet in August 1995 and was appointed Deputy Prime Minister and Minister for Defence. In August 2003, Dr Tan was appointed Deputy Prime Minister and Co-ordinating Minister for Security and Defence.

Dr Tan retired from the Cabinet in September 2005 and was appointed Deputy Chairman and Executive Director of the Government of Singapore Investment Corporation Private Limited (GIC), Chairman of the National Research Foundation and Deputy Chairman of the Research, Innovation and Enterprise Council, and Chairman of Singapore Press Holdings Limited (SPH).

In July 2011, Dr Tan stepped down from his positions at the GIC and SPH to contest in the Presidential Election. He was elected on 27 August 2011, and was sworn in as the seventh President of the Republic of Singapore on 1 September 2011.