Member of the Democratic Action Party (since 2010)

In 2010, Zairil joined the DAP, a component party of Pakatan Rakyat (PR) in opposition to the BN and UMNO federal government. The choice, given that his father was a prominent UMNO politician and that he would be a rare Malay member of the DAP, attracted significant attention. He claimed that UMNO had changed for the worse since his father was a politician, and that "after more than 50 years of UMNO rule, the situation is such that people are being colonised, oppressed by our own people, we do not have any freedom."^[5]

Political Secretary to the Secretary-General

On 23 February 2011, he was appointed as the Political Secretary to Lim Guan Eng, the DAP Secretary-General and Chief Minister of Penang with immediate effect. He henceforth assisted Lim with political matters at party and national level. He was based at the DAP Secretariat in Kuala Lumpur.^[6][7][8]

State Vice Chairman of Penang (since 2013)

In 2013 Penang state party convention, Zairil was elected into the DAP Penang State Committee and subsequently appointed vice-chairman.^[9] In the 2015 state party convention, he was reelected into the committee, placing third highest out of the fifteen elected members with a total vote of 490 out of 760 delegates, he was reappointed to the same position. In the 2018 Penang state party convention, a major surprise emerged after he was defeated, however, he was co-opted into the committee to save his state vice chairmanship.^[10][11] In the 2021 state party convention, he was reelected this time after his defeat in 2018 and retained his state vice-chairmanship.^[12]

Assistant National Publicity Secretary (2013–2022)

At the DAP National Congress in December 2012, Zairil was elected to the Central Executive Committee (CEC) and appointed as the Assistant National Publicity Secretary. The election was re-run in 2013, after a tabulation error that had resulted in his exclusion. He was successful again the second time around.^[13] In November 2017, Zairil was once again re-elected into the CEC and re-appointed as the Assistant National Publicity Secretary.^[14] In the 2013 DAP National Congress, he was elected into the central executive committee and appointed as the National Assistant Publicity Secretary, he was reelected and reappointed in 2017 National Congress. However in the 2022 National Congress, he was not reelected into the CEC and was replaced by Hannah Yeoh Tseow Suan as the Assistant National Publicity Secretary. ^[15]

Penang Institute

From 2012 to 2016, Zairil headed the Penang Institute, a public policy think tank to the State Government of Penang. Zairil has been in the forefront of co-ordinating most of its major activities in propagating the cause of Penang on the national and international arenas, and providing realistic solutions for the economic and social sustenance of the people of the Penang region^[16] Under his leadership, the Institute organised the ASEAN Coalition for Clean Governance (ACCG).^[17] The inaugural conference was held in June 2012, attracting participants from seven countries around the region.

In March 2014, Zairil was promoted to the post of Executive Director^[18] and continued to hold this post until December 2016, when he stepped down to take over the reins of the Football Association of Penang.^[19] He has since been appointed as a Senior Fellow of Penang Institute.^[20]

Member of Parliament (2013–2018)

In the 2013 general election, Zairil won the Bukit Bendera parliamentary seat polling 45,591 votes defeating Barisan National candidate with 32,778 majority. He also gained one of the highest majorities in the election. He was also the youngest candidate to win a federal seat in the election at the age of 30.^[21]

Member of the Penang State Legislative Assembly (since 2018)

In the 2018 Penang state election, Zairil was fielded to contest for the Tanjong Bunga seat where he faced off against Barisan Nasional Penang Chairman Teng Chang Yeow. Considered one of the more challenging seats due to controversies involving the former Tanjong Bunga MLA from DAP who had left the party, Zairil went on to defeat Teng by a margin of 9,343 votes, nearly doubling the margin in the previous election. Following his defeat, Teng announced his retirement from politics.^[22] Zairil was not nominated to contest for his Bukit Bendera seat after holding for a term from 2013 to 2018 and hence transferred to the Penang state level from the federal level.

Member of the Penang State Executive Council (since 2018)

With Pakatan Harapan emerging victorious and being reelected to the power as the Penang state government in the 2018 Penang state election as well as elected to the power as federal government for the very first time in the 2018 general election, then Chief Minister of Penang Lim Guan Eng was appointed as the new Minister of Finance and transferred to the federal level by then Prime Minister Mahathir Mohamad, while National Vice Chairman and State Chairman of Penang of DAP and EXCO member Chow Kon Yeow took over the reins as new Chief Minister of Penang. A new Penang State Executive Council was formed with Zairil being appointed as member for Public Works, Utilities and Flood Mitigation.^[23] During a mid-term review exercise, Zairil took new portfolios and relinquished the old ones, which are the Infrastructure and Transport, with the latter being an additional portfolio.^[24]

Following his re-election to the Penang State Assembly in 2023, Zairil was reappointed as a Penang State Executive Councillor holding the Infrastructure, Transport and Digital portfolios.^[25]