Seymour's End of Life Choice bill was selected from the members' ballot on 8 June 2017 and was put to a referendum in October 2020 in conjunction with the 2020 general election.

[15][16] He was unsuccessful in the electorate, which was held by Helen Clark, the prime minister at the time, and with 1.51% of the party vote ACT returned only two members to parliament, leaving Seymour out.

[23][24] In late 2013, John Banks resigned from his ministerial positions following criminal charges in relation to electoral returns in his bid for the Auckland mayoralty in 2010.

Seymour's selection for Epsom, over former deputy leader and party president John Boscawen,[14] was described by political commentators as the "clean slate" choice[28] and a "fresh face".

[40] In October 2015, a Labour Party member's bill to make parliamentary under-secretaries subject to the Official Information Act passed its first reading in Parliament.

[60][61] An amendment to the bill, which included the requirement that it be approved by a binding referendum before it would take effect, passed prior to its third reading with 63 votes in favour and 57 opposed.

[63] In an interview on the day of the third reading, Seymour said that he was confident that the public would vote to put the act into law, noting that "there was overwhelming support and it should easily pass the referendum.

[84][85] In response, Labour's deputy leader and Te Tai Tokerau Member of Parliament Kelvin Davis alleged that criticism of the iwi-led checkpoints was motivated by anti-Māori racism.

[87][88] The two politicians subsequently reconciled and joined forces to raise NZ$60,000 for the Prostate Cancer Foundation by auctioning a signed and framed copy of the Prime Minister's remark.

[100] In response, Porirua College deputy principal John Topp and attendance officer Mose Skipworth defended the school lunches programme and said that scrapping it would lead to an increase in truancy.

[100][101] On 14 March 2024, Seymour visited Freyberg High School in Palmerston North and met with staff members including Principal Graeme Williams to discuss truancy.

The Board is headed by St Cuthbert's College principal Justine Mahon, with other notable members including Glen Denham and Professor Elizabeth Rata.

Under the revised scheme, 10,000 pre-schoolers in low-equity, non-profit early childhood centres would be eligible for free morning tea and lunch five days a week at a cost of $4 million.

[110][111] In late September 2024, Seymour confirmed that the Government would prosecute parents for persistent truancy and remove teacher-only days during school term time.

Schools would receive funding and resources to either prepare their meals internally, iwi/hapū providers and external suppliers including Gilmours, Foodstuffs, Watties and Hellers.

The Regulatory Standards Bill has been crticised by University of Auckland law Professor Jane Kelsey, who said it would circumscribe scrutiny and prioritised property rights over other considerations including the Treaty of Waitangi, the environment and workplace safety.

By contrast, New Zealand Initiative senior research fellow Bryce Wilkinson argued that good quality legislation was needed to protect personal autonomy and property.

[121] Seymour has embraced libertarian social policies since becoming party leader, such as supporting the legalisation of euthanasia, and introducing the End of Life Choice Act 2019.

[127][128][129] Seymour has increasingly caused controversy for his outspoken views, which include comparing co-governance with apartheid,[130][131] opposing Māori vaccination prioritisation,[132][133] and a joke about sending Guy Fawkes to blow up the Ministry of Pacific Peoples.

[139] In response to the Israel–Hamas war, Seymour as ACT Party leader issued a statement expressing solidarity with Israel and condemning Hamas' actions as terrorism.

[140][141] In response, Prime Minister Hipkins issued a statement condemning Hamas for targeting civilians and taking hostages in violation of international humantiarian principles.

[147][148][149] There has been strong opposition to the proposed referendum by those who view it as divisive or potentially causing civil disorder, and it is highly unpopular on the political left – especially among Māori, but also within the centre-right of the National Party (former prime minister Jim Bolger is such an opponent).

[6] Leaked advice from the Ministry of Justice suggested that the bill was "highly contentious" due to "the fundamental constitutional nature of the subject matter and the lack of consultation with the public on the policy development prior to Select Committee".

[156] In September 2021, Seymour caused a controversy after releasing a special COVID-19 vaccination appointment access code meant exclusively for Māori people in Auckland to his followers on Twitter.

[135] In a 2023 interview with Mihingarangi Forbes, Seymour was questioned about his links to the Atlas Network, an American think tank and policy institute known for its climate change denial.

[170] A clip of Seymour during his time working for the Frontier Centre for Public Policy, in which he spoke with a deliberately acquired Canadian accent, subsequently went viral.

[173] Seymour shrank the budget for free school lunches, a programme introduced by the previous Sixth Labour Government that he has long opposed.

[180] By contrast, Labour's education spokesperson Tinetti criticised the National-led government for allegedly prioritising tax cuts over proper nutrition for children.

[179] On 9 February 2025, Seymour acknowledged that he had written a letter to Auckland District Commander Karyn Malthus in April 2022 complaining about former eye surgeon Philip Polkinghorne's treatment by Police during the course of their investigation into the death of his wife Pauline Hanna.

In November 2024, he announced he had been dating Alexandra Martelli, an Auckland property buyer for the last two years, adding that he was "effectively married to Parliament" which gets in the way of starting a family.