Key was expected to contest for a fourth term of office at the 2017 general election, but on 5 December 2016 he resigned as prime minister and leader of the National Party.

[6] In foreign policy, Key withdrew New Zealand Defence Force personnel from their deployment in the war in Afghanistan, signed the Wellington Declaration with the United States and pushed for more nations to join the Trans-Pacific Partnership.

[10][19] Some co-workers called him "the smiling assassin" for maintaining his usual cheerfulness while sacking dozens (some say hundreds) of staff after heavy losses from the 1998 Russian financial crisis.

At the 2002 general election Key won the seat with a majority of 1,705, ahead of Labour's Gary Russell, with Neeson, now standing as an independent, coming third.

[27] While Keys ambition to become leader had been telegraphed from early in his political career, he was now beginning to rate highly on preferred prime minister polls.

Brash's resignation followed controversies over an extramarital affair, and over leaked internal National Party documents that were later published in the book The Hollow Men.

[24] In his maiden speech as National Party leader, Key spoke of an "underclass" that had been "allowed to develop" in New Zealand, a theme which received a large amount of media coverage.

[24] He relented on his stance in opposition to Sue Bradford's Child Discipline Bill, which sought to remove "reasonable force" as a defence for parents charged with prima facie assault of their children.

Key declaring that he had left Elders months before the event, that he had no knowledge of the deal, and that his interview with the Serious Fraud Office (SFO) during the investigation into the affair could only have helped to convict the people involved.

[5] In January 2009, after addressing Chinese New Year celebrations at the Greenlane ASB Showgrounds, Key tripped after coming down a small set of stairs in front of cameras, leaving him with a broken right arm and "embarrassed".

The agreement signalled an increase in the strategic partnership between the two nations and covered areas of co-operation including nuclear proliferation, climate change and terrorism.

[55] On 22 February 2011 a 6.3 magnitude earthquake struck Christchurch, causing widespread damage to the city region and significantly affecting the national economy.

Political opponents accused Key and his government of hypocrisy; he later apologised, calling it a "sloppy" deal, effectively placing most of the blame on his chief of staff.

[68][69] National won the election, but New Zealand's credit rating was subsequently downgraded anyway – by two different agencies – Standard and Poor's and Fitch Group.

[75] As prime minister, Key was directly responsible for the GCSB,[76] which is not allowed to spy on New Zealand citizens – and Dotcom had been granted permanent residency.

"[77] It subsequently came to light that Deputy Prime Minister Bill English had been asked by the GCSB to sign a "ministerial certificate" suppressing details of the bureau's involvement in the case while Key was overseas – the only time this had been done in the last ten years.

[84][85] There he accused rival candidates Spain and Turkey of using aid money to buy votes from small African countries, and said New Zealand would not be spending its way onto the Council.

[88] In April 2013, whilst visiting Chinese president Xi Jinping in Beijing, Key made headlines by suggesting New Zealand would back any United States or Australian military action against North Korea.

The prime minister was challenged over his criticism of Helen Clark's government's response to the housing crisis during the 2008 campaign, but reluctance to take a stand now it had worsened considerably.

[108] In January 2017, US President Donald Trump signed a presidential memorandum to withdrawing the United States' signature from the agreement, making its ratification virtually impossible.

[109] In February 2016, Key reached an agreement with Australian Prime Minister Malcolm Turnbull to grant New Zealanders living in Australia a pathway to citizenship if they were earning five times over the average wage.

[124] In 2008 Key voted for an attempt to raise the legal drinking age from 18 back to 20,[125] but ignored a Law Commission recommendation to increase levies on alcohol.

[132][133] TVNZ journalist Jack Tame described Key's views on the Government's handling of COVID-19 as provocative but praised his five-point plan as a "collection of sensible ideas worthy of consideration.

[135][136] As a first-term MP in 2003, Key criticised the Labour-led government's stance on the Invasion of Iraq, claiming that New Zealand was "missing in action" by failing to support its ANZUS allies, the United States and Australia.

[138] In August 2022, Key described Speaker of the U.S. House of Representatives Nancy Pelosi's visit to Taiwan as "reckless" and provocative towards China during an interview with TVNZ journalist Jack Tame.

"[139][140] In early October 2024, Key opined that Donald Trump was better for the economy while expressing disagreement with his "isolationist" America First foreign policy during the leadup up to the 2024 United States presidential election.

[152] In a 2002 interview, he said that "some form of orientation towards privatisation" in health, education and superannuation, such as giving firms tax breaks for employer super schemes, made sense.

[153] After his party won a plurality in the 2011 election, Key rejected claims that the National Government lacked a mandate to partially privatise state-owned assets.

Key owns a Guimbal Cabri G2, which he has customised with the proposed alternative New Zealand flag design, three white rabbit emblems for good luck, and his personal callsign, ZK-IJK.

[165] Key was appointed a Knight Grand Companion of the New Zealand Order of Merit, in recognition of "services to the State", in the 2017 Queen's Birthday Honours.