After qualifying as a builder, he retrained as a teacher and taught woodwork, technical drawing and Māori, over a period of twelve years, at Ellesmere College, and at his alma mater, St Bede's.

In the 1996 election he contested the nearby seat of Ilam, a longstanding conservative bastion, and won by a comfortable margin.

In 2002, a District Court judge found in favour of Able that Brownlee had "used excessive and unnecessary force on Abel when he tried to remove him from a staircase handrail".

[11] By 2003, Brownlee was seen by Labour Party MP Phil Goff and Scoop columnist Paulo Politico as a potential challenger to English's leadership.

Initially, Smith alleged that while he was on stress leave, "a campaign to oust me was conducted in the media while I was under the leader's instructions to make no comment.

"[20] Audrey Young wrote in the New Zealand Herald that Brownlee and Murray McCully were rumoured to have been behind the campaign to oust Smith as deputy leader.

Brownlee's approach to this portfolio involved criticising the government's policies regarding perceived special treatment for Māori, an issue at the core of National's 2005 election manifesto.

In April 2013, Brownlee was represented New Zealand in London at the funeral of former British Prime Minister Margaret Thatcher.

[27] In August 2009, Brownlee was criticised by Forest and Bird Spokesperson Kevin Hackwell for playing down government discussions to possibly allow more mining within conservation areas.

[29] In early December 2009, Forest and Bird released a leaked document that included the proposal to remove part of the conservation status of Mount Aspiring National Park to allow mining.

[30] The result of the controversy was that the government decided not to explore considerations amongst significant debate on the issue in the House, in submissions to the Select Committees and within the National Party's own parliamentary caucus.

An additional announcement from Conservation Minister Kate Wilkinson pronounced that future National Park land would receive protections, stating that, "This is an added layer of protection for New Zealand's most highly valued conservation land..."[32] As the Government's most senior Christchurch-based MP, Brownlee led the Government's work in earthquake recovery after the 2010, 2011 and 2016 earthquakes.

[34] On 14 September 2010, Brownlee introduced the Canterbury Earthquake Response and Recovery Act 2010 into the house with leave to pass the legislation in one sitting.

[35] Brownlee had little sympathy for attempts to preserve heritage buildings, saying not long after the 2011 quake: "My absolutely strong position is that the old dungers, no matter what their connection, are going under the hammer.

"[36] In 2012, it was reported that the idea of using part of Christchurch's residential red zone for an international rowing regatta course known as East Lake had found the support of Brownlee as Earthquake Recovery Minister.

[37] In September 2012, Brownlee accused residents in Christchurch's newly created TC3 zone of "carping and moaning" for comments they made in a survey conducted by the main local newspaper.

An official inquiry found that Brownlee and two of his aides had evaded airport security screening by entering a departure lounge through an exit door while in a rush to board a domestic flight.

[42][44] From 2018 to 2020, Brownlee served in Opposition as Shadow Leader of the House, and was the National Party Spokesperson for Disarmament, NZSIS, and GCSB.

[48][49] During the 2020 New Zealand general election, Brownlee lost his seat of Ilam to Labour candidate Sarah Pallett by a final margin of 3,463 votes.

[57] In early November 2023, Brownlee accompanied the caretaker Deputy Prime Minister, Carmel Sepuloni, to the 2023 Pacific Islands Forum in his capacity as National’s foreign affairs spokesperson.

[61] In November 2024, Brownlee's initial decision to bar Newsroom journalist Aaron Smale from attending the National Apology ceremony at Parliament for survivors of abuse in state and faith-based care attracted criticism from both survivor groups and the Parliamentary Press Gallery, the latter of whom appealed the decision.

On 11 November, Brownlee reversed the ban and permitted Smale access to the National Apology on the condition that he was accompanied by a fellow Newsroom journalist.

Earlier that day, RMA Reform Minister Chris Bishop had submitted an amendment paper with a large number of changes to the proposed legislation during the Committee of the House stage of the Fast-Track Approvals Bill.