Fifth Labour Government, 1999–2008

When the Labour Party won power in the 1999 general election, Dyson was appointed to a number of minor ministerial roles, including Disability Issues and Associate Health and Associate Social Development. However, she resigned them on 31 October 2000 after being caught drink driving.^[6] She regained most of her ministerial responsibilities on 4 June 2001.^[7] She acknowledged after her resignation that she had been convicted and fined for possession of cannabis when she was a teenager stating "I find it sickening that some 25 years later someone has anonymously passed this information to journalists."^[8]

As Minister for Disability Issues, she led the development of what would become the New Zealand Sign Language Act 2006, which gave New Zealand Sign Language the status of an official language of New Zealand. In her valedictory statement in 2020, Dyson reflected on the Act: "I regret that it wasn't more prescriptive in its implementation, because its roll-out has been slower than it could have been. That should be fixed."^[9]

In a reshuffle on 31 October 2007, Dyson was promoted to Minister for Social Development, which she held until the Clark government lost power at the 2008 general election. Despite the swing against Labour at that election, Dyson won the new Port Hills electorate with an increased margin.^[10][11]

Opposition, 2008–2017

The National Party won the 2008 election, putting Labour in Opposition where it would remain for the next nine years. During this time Dyson held a range of portfolios, including health (2008–2011), internal affairs (2011–2013), conservation and disability issues (2013–2015), Canterbury Earthquake Recovery (2013–2014) and senior citizens (2013–2017).^[12][13] She was also deputy chair of the Health select committee (2008–2011) and chair of the Government Administration select committee (2011–2017).

In December 2009 Dyson's Resource Management (Requiring Authorities) Amendment Bill, which would amend the Resource Management Act 1991 to reintroduce a public interest test for projects seeking requiring authority, was drawn from the member's ballot.^[14] The bill was defeated at its first reading.^[14]

Dyson was criticised in December 2015 for describing National's Speaker David Carter as "incompetent, biased... lazy [and] sexist" on Twitter.^[15][16]

Sixth Labour Government 2017–2020 and retirement

Dyson had been positioned to be Deputy Speaker of the House of Representatives (to Trevor Mallard) if Labour won the 2017 general election.^[17] While Labour was able to form a Government (in coalition with New Zealand First), the National Party's Anne Tolley was appointed as Deputy Speaker instead. Dyson was put in the role of Labour's Senior Whip.^[18] However, when the Assistant Speaker Poto Williams was appointed as a Minister outside Cabinet in July 2019, Dyson was named as her replacement.^[19]

Dyson was also chair of the Abortion Legislation Committee (a special select committee that examined the Abortion Legislation Bill) and a member of the Epidemic Response Committee (which considered the government's response to the COVID-19 pandemic).^[20]

In March 2019, Dyson indicated that she would not seek re-election at the 2020 general election.^[21] While the Port Hills electorate was disestablished for that election, Labour's candidate for the replacement electorate of Banks Peninsula was Tracey McLellan.^[22]

In the 2021 Queen's Birthday Honours, Dyson was appointed a Companion of the Queen's Service Order, for services as a member of Parliament and to people with disabilities.^[23]

In March 2023, Dyson was accused of not being politically impartial in her roles as deputy chair of the Earthquake Commission and Fire and Emergency New Zealand as is the expectation of public servants and government-appointed board members. She admitted to not having read the code of conduct governing her position as a Crown entity board member. She said "I'm prepared to review all my social media engagement and reflect on whether it meets the standard. I haven't done that yet," She had written on Twitter "Oh no. It sounds like some cruel junior staffer gave Mr Luxon the wrong speech! #Waitangi2023,"^{[24][25][26][27][28]} Prime Minister Chris Hipkins said "I would certainly expect her to be reading it [Code of Conduct] ... my understanding is she has subsequently been in touch with the relevant minister's office to indicate she will read the code of conduct and she will follow it".^[29]