A general election was held in New Zealand on 8 November 2008 to determine the composition of the 49th New Zealand Parliament. The liberal-conservative National Party, headed by its parliamentary leader John Key, won the largest share of votes and seats, ending nine years of government by the social-democratic Labour Party, led by Helen Clark. Key announced a week later that he would lead a National minority government with confidence-and-supply support from the ACT, United Future and Māori parties. The governor-general swore Key in as prime minister on 19 November 2008. This marked the beginning of the Fifth National Government which governed for the next nine years, until the 2017 general election, when a government was formed between the Labour and New Zealand First parties, with support on confidence and supply by the Green Party.

The Green Party became the third-largest party in Parliament, with nine seats. The ACT Party came joint-fourth (in terms of seats), increasing their number of seats from two to five, and reversing some of their losses from the 2005 election. The Māori Party also won five seats – out of the seven Māori electorates – creating an overhang of two seats. The New Zealand First party, which had seven MPs in the previous parliament, failed to win any electorates or pass the 5 per cent MMP threshold, and therefore won no seats in the new parliament.

In his victory speech, John Key announced the readiness of the ACT, Maori Party and United Future parties to co-operate with the National Party to form the next government, the Fifth National Government of New Zealand. In her concession speech, Helen Clark announced her resignation as the parliamentary leader of the Labour Party. She had led the party since 1993, and had served as prime minister since the 1999 election. 2008 saw several important political figures enter Parliament, including future finance minister Grant Robertson, future National Party leader Simon Bridges, and the next two Labour Prime Ministers, Jacinda Ardern and Chris Hipkins. Former Labour minister Roger Douglas, who stepped down in 1990 returned to parliament in this election but as a member for the ACT Party.

New Zealand elections traditionally occur after September in the third year following the last election, and snap elections occur rarely; the only three elections out of sync in the period of 1948 to 2008 took place in 1951, 1984 and 2002—and the last two came only a few months early. Convention in New Zealand expects Parliaments to run for a full three years unless the government loses the confidence of the House, although this has not happened since 1911.

The Constitution Act 1986 defines the term of Parliament as "three years from the day fixed for the return of the writs issued for the last preceding general election of members of the House of Representatives, and no longer". Since the writs for the 2005 election were returned on 6 October 2005, the ensuing 48th New Zealand Parliament expired on 6 October 2008, making 15 November the final possible date for the 2008 general election.

On Friday 12 September 2008, Prime Minister Helen Clark announced that the general election would take place on 8 November 2008. This set the full election timetable as:

Nineteen registered political parties contested the party vote:

The following parties either disappeared during the previous parliament's term (2005 to 2008), or did not contest the 2008 elections for other reasons.