After completing his training in Wisconsin, he returned to Singapore as the first and only infectious diseases consultant at National University Hospital. In 2000 he became one of the committee members of the Action for AIDS Singapore, the only HIV/AIDS agency in Singapore first founded in 1988.[7] In 2001 Tambyah became an associate Professor of Medicine.
During the SARS outbreak in 2003, Tambyah helped establish the NUH Division of Infectious Diseases, with Professor Dale Fisher and trainee Dr Louis Chai joined in December 2004. Since then, the Division has grown and currently includes 13 consultants, a resident physician and 2 senior residents.[8]
In 2011, Tambyah became the President of the Asia-Pacific Society of Clinical Microbiology and Infection, and led the Singapore Society of Infectious Diseases from 2011 to 2015.[9] Tambyah became a full professor on 5 July 2013.[10]
On 6 December 2020, Tambyah received a Red Ribbon Award by Action for AIDS Singapore for his contributions to HIV-related causes.[13]
On 5 October 2021, Tambyah was recognised as one of the four eminent senior clinicians to receive the Distinguished Senior Clinician Award as conferred by the Ministry of Health in Singapore.[14]
On 20 December 2022, Tambyah became the new President of the International Society of Infectious Diseases Executive Committee, replacing Alison Holmes who would currently serve as its immediate past-President.[15] This eventually fulfilled the two-year speculation as he has become the first Singaporean President of the International Society of Infectious Diseases.
Tambyah was the recipient of the Commendation Medal (COVID-19) and the COVID-19 Resilience Medal[16] of the National Awards (COVID-19) awarded by the Prime Minister's Office to individuals and teams in recognition of their public spirit and contributions to Singapore's fight during the COVID-19 pandemic in Singapore for over two years.[17]
Activism
Tambyah was noted to be one of the founding members of MARUAH Singapore, a human rights organization which was founded in 2007 in Singapore. Due to the limitations of civil society activism, he eventually left the organization to join politics.[18]
On 26 September 2017, he was elected as Chairman by the CEC members during the Singapore Democratic Party 18th Ordinary Party Conference, replacing Wong Souk Yee.[21][22]