An electorate called Selwyn existed between 1866 and 1919. A Selwyn electorate also existed between 1946 and 1972 and again from 1978 until it was absorbed by Rakaia for the first MMP election in 1996. The latest version of the Selwyn electorate was created for the 2008 election. This followed a review of electoral boundaries conducted after the 2006 Census, because of a general northwards population movement in the South Island. Even though the number of South Island electorates is fixed, the decline in the population of electorates from Rakaia south has resulted in the boundaries of electorates from Invercargill north to Rakaia shifting further northwards. Due to the rapid growth of Selwyn relative to Christchurch, the 2013 redistribution had Selwyn losing Halswell and Westmorland to Port Hills and Harewood to Waimakariri while regaining the towns of Rakaia and Chertsey back from Rangitata. Data from the 2018 census showed Selywn's population had continued to grow – it had the largest discrepancy of any electorate – and so the electorate would need to lose further area for the 2020 boundaries. It shed an area around Hornby South to, the Banks Peninsula to the recreated, the area west of the Rakaia to, and an area around Christchurch Airport to.
Voting history
The dominant topic for the 1875 election was the abolition of the Provinces. William Reeves, the incumbent, favoured the retention of the provincial system of government, while his opponent, Cecil Fitzroy, was an abolitionist. Fitzroy, who was 31 years old and 20 years Reeves' junior, narrowly won the election. Edward Lee acted as returning officer for the election. In the, John Hall was returned unopposed. In the, Hall beat R. Lockhead by 467 to 169 votes. In the, Alfred Saunders, Thomas Hamilton Anson, and William Jerrington Popple received 536, 485 and 237 votes, respectively. The electorate is one of the National Party's safest seats. National have held the seat, whenever it has existed since it was first recreated in 1946. The incumbent MP is Amy Adams, who has received between 60% and 70% of the electorate vote in the four elections since its latest recreation in 2008. In 2011, the candidate for the other major New Zealand party, Labour, received less than 11% of the electoral vote and came third, behind the Greens in the 2011 election. In that election, the only polling booths where Adams didn't receive the most votes were Arthur's Pass and Diamond Harbour.
Members of Parliament elected from party lists in elections where that person also unsuccessfully contested the Selwyn electorate. Unless otherwise stated, all MPs terms began and ended at general elections.
