The Wanganui Campaign was a brief round of hostilities in the North Island of New Zealand as indigenous Māori fought British settlers and military forces in 1847. The campaign, which included a siege of the fledgling Wanganui settlement—then known as Petre—was among the earliest of the 19th century New Zealand Wars that were fought over issues of land and sovereignty.
The Wanganui settlement had been established by the New Zealand Company in 1840 on land supposedly bought by William Wakefield in November 1839. By 1845 the settlement had grown to about 200 people and about 60 houses. The settlement was surrounded by about 4000 Māori and although settlers engaged in trade with them for food, there was also friction over their occupation of land which some Māori chiefs denied having sold, with New Zealand Company surveyors reporting obstruction and harassment. Settlers were also nervous about a possible spread of hostilities from the Hutt Valley over disputed land occupation, where one of the most prominent fighters was Te Mamaku, a principal chief of the Ngāti-Hāua-te-Rangi tribe of the Upper Wanganui.
In December 1846, 180 soldiers from the 58th Regiment and four Royal Artillery men were landed at Wanganui with two 12-pounder guns and began fortifying the town, building the Rutland Stockade on a hill at the town's northern end and the York Stockade towards the south. Another 100 soldiers from the Grenadier Company of the 65th Regiment arrived the following May. The establishment of the garrison heightened Te Mamaku's expectations of government intervention, and he vowed he would protect settlers but fight the soldiers.
On 16 April 1847 a minor chief of the Wanganui people was accidentally shot by a junior army officer, suffering a head injury. A small party of Māori decided to exact utu (revenge, or recompense) for the blood-letting and attacked the home of a settler named Gilfillan, severely wounding him and a daughter and killing his wife and three children with tomahawks. Five of the six killers were captured by lower Wanganui Māori; four were court-martialled in Wanganui and hanged at Rutland Stockade. The execution prompted a further revenge attack. About 500 or 600 heavily armed Māori formed a taua (war party) that swept down the Wanganui River in a procession of war canoes in early May, initially plundering and burning settlers' houses and killing cattle. The warriors also killed and mutilated a soldier from the 58th Regiment who ventured out of the town. The town's residents abandoned their homes at night to begin sleeping in a small group of fortified houses.
On 19 May Te Mamaku's warriors made their first attack on the town, approaching from the west and north, effectively besieging the settlement. More homes were ransacked. A British gunboat fired from the river, mortally wounding Maketu, a chief, and rockets were also fired at them from two armed boats on 24 May when Governor George Grey arrived with Tāmati Wāka Nene, future Māori king Te Wherowhero and several other northern chiefs in a bid to defuse the situation.
In June reconnaissance missions were mounted up the valley of the Wanganui River from the garrison—which now contained 500 to 600 soldiers—resulting in some minor skirmishes. By mid-winter Māori leaders, recognising they had reached a stalemate and conscious that their potato-planting season was approaching, decided to launch a full attack on the town to draw troops from their forts.
On 20 July about 400 Māori fighters approached the town from the low hills inland, occupying a ridge at St John's Wood where they had dug trenches and rifle-pits and thrown up breastworks. About 400 imperial soldiers commanded by William Anson McCleverty became involved in a series of skirmishes along a narrow pathway through swampy ground. After being bombarded with artillery fire, Māori forces charged on the troops, who responded with a bayonet charge, halting the Māori advance. Māori withdrew to the trenches and breastworks, maintaining fire on the British troops until nightfall. Three British soldiers died and one was wounded in the clash; three of their enemy were killed and about 12 wounded in the so-called Battle of St John's Wood.
On 23 July Te Mamaku's forces appeared again, exchanging fire with British forces before retiring upriver to their stronghold near Pipiriki. In February 1848 Grey negotiated a peace settlement with Te Mamaku.
Twelve years of economic cooperation and development followed, with the gradual alienation of yet more Māori land which led to more conflict.