Porirua is a city and a harbour in New Zealand situated immediately north of Wellington, with the city centres about 20 km apart. The city completely surrounds the Porirua Harbour, part of which has world-class estuarine values.
The name "Porirua" is of Maori origin. It is possibly a variant of "Pari-rua", a reference to the two arms of the Porirua Harbour. It was the name given in the 19th century to a land registration district that stretched from Kaiwharawhara (or "Kaiwarra") (on the north-west shore of Port Nicholson) northwards to and around the Porirua Harbour. A road climbing the hill from Kaiwharawhara towards Ngaio and Khandallah is still called "Old Porirua Road".
In the 19th century a small Maori settlement existed, and a small European village grew up, partly because of the need for a ferry across the harbour. Late in that century the Porirua Mental Hospital was erected on the hill south-west of the village.
Originally planned to become a satellite city to Wellington with State housing in the late 1940s, Porirua has grown to a city population approaching 55,000. Major territorial additions to the city were made in 1973 and 1988 as part of the reduction and eventual abolition of the Hutt County.
Suburbs include Ascot Park, Cannons Creek, Elsdon (named after writer Elsdon Best), Onepoto, Paremata, Pauatahanui, Plimmerton, Pukerua Bay (where film-maker Peter Jackson grew up), Ranui Heights, Takapuwahia (originally a Ngati Toa settlement), Titahi Bay, Waitangirua, and Whitby. Rural localities include Judgeford and Horokiri.
Local government in the area is shared by the Porirua City Council and the Wellington Regional Council.