Te Wherowhero was born in Waikato towards the end of the eighteenth century. He was the eldest son of a Waikato warrior chief, Te Rauangaanga, and Parengāope of Ngāti Koura. He belonged to the senior chiefly line of Ngāti Mahuta, and was descended from the captains of the Tainui and Te Arawa canoes. Te Wherowhero had four wives, Whakaawi, Raharaha, Waiata and Ngāwaero. His children were Matutaera (later known as Tāwhiao), Mākareta Te Otaota and Tīria.
Te Wherowhero grew up in the period of peace that followed the great victory of Waikato over Ngāti Toa in the battle called Hingakākā, at Te Mangeo, near Lake Ngāroto. He was taught traditional lore by his father and later learned sacred knowledge at Te Papa-o-Rotu, the Waikato whare wānanga at Whatawhata. He also trained as a warrior, and when his relative Te Uira was killed by Ngāti Toa, he took part in warfare against them. He is said to have instigated the killing of Marore, a wife of Te Rauparaha, while she was visiting relatives in Waikato about 1820. After revenge killings by Ngāti Toa, an army of Waikato and Ngāti Maniapoto warriors invaded Kāwhia in 1820, and defeated Ngāti Toa at Te Kakara, near Lake Taharoa, and Waikawau, south of Tīrua Point. Te Rauparaha was then besieged at Te Arawī, near Kāwhia Harbour, and after negotiations it was agreed that Ngāti Toa should cede their lands to Waikato and depart for the south. They were allowed to leave and at first went to Te Kaweka, in northern Taranaki.
Te Wherowhero then led a large army in pursuit. He was also going south to the aid of Peehi Tūkorehu, a Ngāti Maniapoto leader, whose war party was besieged at Pukerangiora, on the Waitara River, by Taranaki tribes. In late 1821 or early 1822 the Waikato army suffered a military disaster at Motunui; against Te Wherowhero's orders it charged a feigned retreat of Ngāti Toa and its allies. Te Wherowhero refused to join the retreat that followed and remained by the body of a slain Waikato chief, where Ngāti Toa and their Ngāti Mutunga allies found him. A man of Ngāti Mutunga would have shot him, but was stopped by Te Rauparaha. Te Wherowhero then fought a number of chiefs in single combat, armed only with a digging implement. Waikato forces returned to join him and both armies retired. It is said that at night Te Wherowhero approached the Ngāti Toa camp and asked Te Rauparaha for his advice. Te Rauparaha directed him south to Pukerangiora, to avoid a Taranaki army to the north. Te Rauparaha's assistance to Te Wherowhero was probably due to their common descent from the people of the Tainui canoe. Te Wherowhero went to Pukerangiora and raised the siege of the Waikato warriors there before returning to Waikato. He returned in time to lead Waikato against an invasion by the musket-armed Ngāpuhi of Hongi Hika.
Hongi Hika was seeking revenge for the deaths of several relatives at the hands of Waikato allies in Tāmaki and Hauraki. He led 3,000 warriors to the Waitematā Harbour; they dragged their canoes to the Manukau Harbour, and went from there to the Waikato River by way of the Awaroa Stream. Waikato delayed the invaders by felling trees into the stream. They concentrated their defence at Mātakitaki pā, where 10,000 people gathered under Te Wherowhero's command in May 1822. When Ngāpuhi attacked, a panic seized the defenders, many of whom had not experienced musket warfare before. There was a rush to escape the pā and many people were trampled to death. Te Wherowhero led a defensive fight, at one point single-handedly.
After the fall of the pā, Ngāpuhi split into small groups to hunt for fugitives. At Ōrāhiri, near Ōtorohanga, a large group of Ngāti Mahuta women were captured. Te Wherowhero had retreated towards the Rangitoto Range and was cautiously moving back down the Waipā River when he met an old woman who had escaped. He sent her back to tell the women that they would be rescued as soon as the morning star rose. At this hour the enemy warriors were asleep, except for one who was drinking from the river. He was quietly drowned and the rest of that group of Ngāpuhi were killed. Waikato settled further south for several years, for fear of further Ngāpuhi attacks. Te Wherowhero lived at Ōrongokoekoeā on the upper Mōkau River. His wife, Whakaawi, gave birth there to their son Matutaera. When peace was made with Ngāpuhi in 1823, Waikato gradually returned to their homes. The peace was cemented by the marriage of Te Wherowhero's close relative, Kati, to Matire Toha of Ngāpuhi. Their daughter was Te Paea.
Hongi Hika came to Waikato again in 1825 in pursuit of Ngāti Whātua fugitives, but he did not attack Waikato. However, in 1826 Pōmare I led Ngāpuhi to invade Waikato while Te Wherowhero was at Taupō. Te Wherowhero wished to go and meet Pōmare, but was dissuaded by Te Kanawa, who feared treachery. Pōmare and his army went up the Waipā River and were defeated, and Pōmare killed, at Te Rore. In 1827 Waikato forces went to Tāmaki to assist Ngāti Paoa against a Ngāpuhi attack, and Te Wherowhero then led a canoe fleet to attack Ngāpuhi at Whāngārei. Waikato won a battle at Ōparakau, after which peace was arranged and Waikato returned home. On this expedition Te Wherowhero wore a cloak of red kākā feathers, from whose colour his name is sometimes said to be derived.
Warfare with Ngāti Hauā about 1830 forced Ngāti Maru north towards Hauraki, and by this time Ngāti Raukawa had migrated south to Manawatū. This left Waikato free to seek revenge for their defeat at Motunui by Taranaki tribes. In 1831 Te Wherowhero led an expedition into Taranaki and attacked Te Ati Awa. They took refuge at Pukerangiora, but did not have time to gather food for a long siege. After three months the pā fell when its inhabitants attempted to escape in daylight. They were massacred, and many were eaten. It is said that Te Wherowhero killed 150 prisoners with his mere, Whakarewa. His army, however, failed to take the pā at Ngamotu, near present day New Plymouth, and returned home.
Ngāpuhi raided Waikato again in 1832 but were driven off by 3,000 Waikato warriors, most of them armed with muskets. The firearms had been obtained from the trader J. R. Kent, who had settled at Kāwhia and married Tīria, the daughter of Te Wherowhero. The name Pōtatau may have been taken by Te Wherowhero at the time of this marriage.
Te Wherowhero continued his attacks on Taranaki tribes between 1833 and 1836. He had been provoked by a raid on the Mōkau River by Te Ati Awa. He besieged several pā, with varying degrees of success. Mikotahi pā, on an island near Ngamotu, was supplied by sea and proved impregnable. At Te Namu, near Ōpunake, Ngāti Ruanui drove off five assaults by Waikato, but Te Ruaki pā, near Hāwera, was forced to surrender after a siege of three months. After an unsuccessful attack on Waimate pā, at the mouth of the Kapuni Stream in 1836, Te Wherowhero made peace with the Taranaki people and withdrew, saying that he would not return.
Missionaries arrived in Waikato in the mid 1830s. Their growing influence was demonstrated by the release in 1840 of slaves taken during the Taranaki wars. Although he attended church services, Te Wherowhero was never baptised. In March 1840 Captain W. C. Symonds brought a copy of the Treaty of Waitangi to Manukau, where Te Wherowhero was living at Awhitū. He refused to sign the treaty but was kindly disposed towards the European government. In May 1844 he provided a huge banquet for a great intertribal gathering at Remuera. His influence at the meeting impressed on Governor Robert FitzRoy the fact that Auckland's security depended on Waikato friendship. In the 1840s Te Wherowhero's cottage at Pukekawa, in the Auckland Domain, was the scene of much discussion of issues arising from the signing of the Treaty of Waitangi. He was one of the chiefs who sold land to the government in the Manukau area. However, he protested to Queen Victoria over the 1846 instruction from Earl Grey, secretary of state for the colonies, that all land not actually occupied or cultivated by Māori was to be regarded as Crown property, in contravention of the guarantees of the Treaty of Waitangi. In 1848 Te Wherowhero was one of those who accompanied Te Rauparaha's return to his people at Ōtaki, on his release from government custody. At Governor George Grey's request Te Wherowhero and some of his followers moved to Māngere and in 1849 he signed an agreement to provide military protection for the city of Auckland.
A movement arose in the 1850s to establish a Māori king to protect Māori land from alienation and to make laws to end internal strife. Mātene Te Whiwhi travelled throughout New Zealand seeking a chief of high standing who was willing to be king. Iwikau Te Heuheu Tūkino III, of Ngāti Tūwharetoa, suggested that Te Wherowhero should be approached, and his choice was supported by Wiremu Tāmihana, of Ngāti Hauā. Te Wherowhero was reluctant to take on the role of peacemaker while the death of one of his relatives, Rangiānewa, at the hands of Ngāti Hauā in 1825, was unavenged. Peace was made, however, and after lengthy negotiations Te Wherowhero accepted the kingship, and was installed at Ngāruawāhia in 1858. In his speech of acceptance he stressed the spirit of unity symbolised by the kingship, likening his position to the 'eye of the needle through which the white, black and red threads must pass.' He enjoined his people to 'hold fast to love, to the law, and to faith in God.'
Te Wherowhero never regarded the kingship as being in opposition to the sovereignty of Queen Victoria, and wanted to work co-operatively with the government. Some of his associates, however, sought to prevent or hinder government activities in areas which supported the King. Te Wherowhero opposed their levying of port dues on ships at Kāwhia Harbour, and threatened to leave Waikato and return to Māngere if tribute continued to be demanded from government mail canoes using the Waipā River.
Te Wherowhero had been much consulted by governors George Grey and Thomas Gore Browne on matters concerning Māori. However, after his acceptance of the kingship he was increasingly estranged from the governor's confidence. As land disputes increased in number and severity Te Wherowhero was in many cases forced into a position of opposition to government policy.
Pōtatau Te Wherowhero died at Ngāruawāhia on 25 June 1860. Many tribes gathered to pay their last tributes to him. He was succeeded as King by his son Tāwhiao.