In October 2017 when Jacinda Ardern became Prime Minister of New Zealand, Nash entered Labour Cabinet, with a portfolios of Police, Revenue, Small Business and Fisheries.

[4] In 2005, Nash was a Labour candidate for the safe National seat of Epsom, placing third behind Rodney Hide and Richard Worth; having been directed by then-Prime Minister Helen Clark to ask Labour supporters to vote for the National candidate, Richard Worth, in a strategy designed to defeat ACT MP, Rodney Hide.

The tactic didn't work, with Hide winning; though at 9,915 Labour received the highest number of party votes in this electorate since the introduction of the MMP parliamentary system in 1996.

[9] On 15 June 2010, Opposition Leader Phil Goff appointed Nash to be portfolio spokesperson for Forestry, a position formerly held by Mita Ririnui.

However, Nash resigned after just four months into the job and returned to his home town of Napier, citing the birth of his new child and focusing on winning back the electorate there.

[14][15][16] Nash retained the Napier electorate in 2017, increasing his majority and becoming only the second Labour MP after Damien O'Connor to win and hold a seat off the National party this century.

[21] In mid November 2021, Nash claimed that farming advocacy group Groundswell NZ's website promoted racism and vaccine hesitancy in response to a question by ACT Member of Parliament Mark Cameron.

In response to Stuart's remarks, Groundswell co-founder Bryce McKenzie emphasised the group's efforts to combat racism and vaccine hesitancy among its ranks.

[24] Nash subsequently admitted to a third incident of misconduct where he contacted the Ministry of Business, Innovation and Employment (MBIE) to advocate for a migrant health professional in Napier in September 2022.

In a statement published on Facebook, he stated while his work as a minister in the Ardern Cabinet "has been rewarding, and both intellectually and professionally stimulating, it has also been incredibly taxing on relationships with family and friends."

[33] Newshub reported that the Cabinet office had examined five years worth of Nash's communications and that a senior minister had disputed the inclusion of McCaw's appointment within the probe.

In March 2023, the Labour government had passed the Criminal Proceeds (Recovery) Act 2023, which allowed Police to seize gang leaders' properties, cars, bikes and bling valued at NZ$30,000 or above in compliance with the New Zealand Bill of Rights.

Nash claimed that former Justice Minister Kiri Allan had blocked efforts to introduce tougher anti-gang legislation on the grounds that it targeted Māori people.