[7] He became interested in politics at a young age, once authoring a story in which he served thirteen consecutive terms as President of the United States.

He lists his CV as including the role of general manager corporate and grower services from 2003 to 2006, followed by a move to the position of chief executive at Apata Ltd in January 2006.

[18][19][20][21] Muller left Fonterra and his directorships in June 2014 to campaign for the 2014 general election after being selected as the National Party candidate for the Bay of Plenty electorate.

[29] National lost the 2017 general election and Muller was assigned spokesperson roles in the agriculture, biosecurity, climate change, food safety, and forestry portfolios by new leader Simon Bridges.

Muller's work on the bill earned him respect from across the House and a lasting friendship with Green Party climate change minister James Shaw.

"[36] In May 2020, Muller challenged National Party leader Simon Bridges for the leadership on a joint ticket with Auckland Central MP Nikki Kaye.

[40][41] A One News Colmar Brunton poll released the evening before the coup had Muller with the support of 0.2% of voters as preferred prime minister compared to Jacinda Ardern on 63% and Bridges on 5%.

[44][45] Senior MP Anne Tolley, a conservative, was among those who spoke out in opposition to Muller's leadership challenge, calling it "nutty stuff",[46] announcing that she would be retiring shortly thereafter.

[47] Another National MP, speaking to media on the condition of anonymity, described Muller in contrast to Bridges as a "pale, stale male".

Muller stated former leader Simon Bridges was offered a shadow ministerial role but declined, saying he was taking time to consider his future.

[50] National MP Jo Hayes criticised Muller for the lack of ethnic diversity present in the new frontbench, telling media: "This is not good.

[52] On 27 May, another leak against the leadership was made to Newshub claiming the campaign chair, Gerry Brownlee, had set up an "intelligence unit" to find negative information on political opponents.

[53] As a result of the leaks to media, inability to fend off criticism over his "Make America Great Again" cap display (see below), and allegedly poor television interview performances, Muller was criticised by commentators traditionally supportive of the National Party, including Mark Richardson.

[54] Fellow conservative commentator Mike Hosking opined in his New Zealand Herald column that "Todd Muller's first full day out including Parliament was little short of a disaster.

Referring to the "decent society" policy under the Jim Bolger-led National Party of the 1990s, Muller stated that the New Zealand economy was not "truly internationally competitive or agile enough [or] as green as [it] should be."

An event organiser inadvertently hung the tino rangatiratanga flag upside down behind the podium and Muller accidentally referred to himself as having joined the Labour Party.

[59][60] On 7 and 8 July, Muller moved to sack Hamish Walker after the first-term MP admitted to leaking personal details of COVID-19 patients to the media.

[61] The weekend after, Muller refused to appear on Q+A to discuss the incident and directed his inner circle to focus on National's energy policy to be announced the next week.

[64] In the 2020 New Zealand general election held in October, Muller retained his Bay of Plenty seat, defeating Labour candidate Angie Warren-Clark by a margin of 3,415 votes.

[73] He also admitted that for several years he had been providing inside information about the party to Richard Harman, the proprietor of the political news website Politik.

[74] According to the New Zealand Herald, Collins threatened to have the caucus vote to suspend him if he did not step down, while Chris Bishop urged him to leave with dignity "for the good of the party.

[79] On 21 August 2021, the Bay of Plenty Times published an interview with Muller where he stated that he intended to return to Parliament when it next sat and to serve until the end of the term, despite speculation that he would leave earlier.

[81] In October 2022, Muller also became National's acting spokesperson for agriculture, biosecurity, and food safety after Barbara Kuriger resigned from those positions due to a personal conflict of interest.

[85] In March 2023, Muller announced he would, in fact, leave politics at the 2023 general election, stating that he did not "have enough fire in the belly for the job" and that he would like to spend more time with his family.

[91] He received attention in 2020 for his intention to display a 'Make America Great Again' cap in his Parliamentary office as part of a collection of American political memorabilia, with a Muslim community leader calling on him to leave it at home.

[95] During his valedictory speech, Muller called for New Zealand to be realistic about its ability to address climate change based on its "size, distance from market, infrastructure vulnerabilities, and balance sheet capacity."

Muller has also expressed concern about growing partisanship on issues relating to Māori and the Treaty of Waitangi, which in his view is fuelling a level of political toxicity that is corrosive to our society."