Porirua is a city in the Wellington Region of the North Island of New Zealand, and one of the four cities that constitute the Wellington metropolitan area. It almost completely surrounds Porirua Harbour at the southern end of the Kapiti Coast. Pauatahanui Inlet, the eastern inlet of the harbour, is notable for its world-class estuarine values. The population at the was .
The name "Porirua" has a Māori origin: it may represent a variant of pari-rua ("two tides"), a reference to the two arms of the Porirua Harbour. In the 19th century the name designated a land-registration district that stretched from Kaiwharawhara (or Kaiwara) on the north-west shore of Wellington Harbour northwards to and around Porirua Harbour. The road climbing the hill from Kaiwharawhara towards Ngaio and Khandallah still bears the name "Old Porirua Road".
In the 19th century a small European settlement grew up, partly because of the need for a ferry across the harbour. At the time a small Māori settlement already existed.
The Wellington and Manawatu Railway Company opened a railway line to Porirua in 1885, linking the city with Wellington. The railway reached Longburn (south of Palmerston North) in 1886 to connect with the Government's lines to Taranaki and Napier. With the acquisition of the company by the government in 1908, the line to Porirua formed part of the North Island Main Trunk railway. The railway contributed much to the growth of Plimmerton and Paremata by making day-trips to the beaches from Wellington relatively easy. The line through to Porirua was electrified in 1940 following the construction of the Tawa Flat deviation.
The 1880s and 1890s saw the establishment of the Porirua Lunatic Asylum on the hill south-west of the village. Following the Mental Defectives Act of 1911, the Asylum became Porirua Mental Hospital.
In the late 1940s state planning envisaged Porirua becoming a satellite city of Wellington with state housing. Since then Porirua has grown to a city population approaching 51,000, with state housing no longer in the majority. Major territorial additions to the city occurred in 1973 and 1988 as part of the reduction and eventual abolition of Hutt County.
Substantial industrial areas generally west of the city centre were established in the 1960s and 1970s, dominated by the Todd Motors building (later Mitsubishi), prominent in the panorama below.
On 7 June 1976, New Zealand's first McDonald's restaurant opened in Porirua, on the corner of Cobham Court and Hagley Street. The original restaurant closed on 24 April 2009, and the store relocated to Kenepuru Drive.