A member of the governing People's Action Party (PAP), he has been the Minister of State for Transport, Minister of State for Law since July 2024 and Member of Parliament (MP) representing Bukit Batok SMC and an advisor of Bukit Batok Grassroots Organisation since May 2016.

Pillai joined the People's Action Party (PAP) in 2001 and was the branch secretary to Ong Chit Chung, Member of Parliament for Bukit Batok.

He was part of a five-member PAP team who contested and narrowly lost[4] to the Workers' Party in Aljunied GRC during the 2015 general election.

[1] While serving his National Service, Pillai was a platoon commander in the 2nd Guards Battalion of the Singapore Army.

[4] On 12 March 2016, David Ong, the PAP Member of Parliament for Bukit Batok SMC, resigned, citing a "personal indiscretion".

[12][13][14][15][16] Pillai defeated the Singapore Democratic Party's candidate Chee Soon Juan and secured 61.21% of the votes to win the Bukit Batok by-election on polling day.

After the 2018 cabinet reshuffle, Pillai was appointed Chairperson of Home Affairs and Law Government Parliamentary Committee (GPC) in the 14th Parliament.

[18] He continued to serve as Chairman until 1 July 2024 where he relinquished the Chairmanship to Zhulkarnain Abdul Rahim after taking office as Minister of State.

On 30 June 2020, after submitting his nomination papers for the election, Pillai claimed on social media that there was an online attack against his son, who was convicted of an offence.

[19] During the campaign period, Pillai was criticised by Chee Soon Juan from the Singapore Democratic Party for the fulfilment, delays, and safety issues in his constituency projects.

[23] In his eight years as an MP, Pillai has focused mainly on helping to close significant gaps in Singapore society as well as the country’s laws.