In the 2015 general election, Koh contested in Ang Mo Kio GRC as part of a six-member PAP team and won with 78.64% of the vote.

Koh was elected as the Member of Parliament representing the Yio Chu Kang ward of Ang Mo Kio GRC.

Koh entered politics in January 2013 when he contested as the People's Action Party (PAP) candidate in a by-election in Punggol East SMC triggered by the resignation of its Member of Parliament, Michael Palmer, after it was revealed that he had an extra-marital affair.

Koh thus became a Member of Parliament representing the Yio Chu Kang ward of Ang Mo Kio GRC.

On 23 April 2018, Koh was appointed Deputy Secretary-General of the National Trades Union Congress[12] and he held this position until 15 May 2021.

[13] In the 2020 general election, Koh switched to join the five-member PAP team contesting in Tampines GRC and they won with 66.41% of the vote against the National Solidarity Party.

[16] A Chinese Singaporean of Teochew descent, Koh grew up in a farmhouse at Lorong Cheng Lim in Punggol before he and his family moved to a four-room HDB flat in Toa Payoh.