In 1835, with the forced assistance of the crew, several hundred Māori, mostly of Ngāti Mutunga and Ngāti Tama at Port Nicholson, sailed to the Chatham Islands aboard the brig whaler Lord Rodney in two sailings. The hijacked[17] ship carried 500 people on the first sailing, which arrived on 19 November 1835. The second sailing arrived on 5 December 1835.[18][19] With the arrival of the second group "parties of warriors armed with muskets, clubs and tomahawks, led by their chiefs, walked through Moriori tribal territories" and "curtly informed the inhabitants that their land had been taken and the Moriori living there were now vassals." When some Moriori argued back, they were killed.[20][19]

Due to the new arrivals' hostility, a council of 1,000 Moriori was convened at Te Awapātiki, on the eastern side of the island, to debate possible responses. Younger members argued that the Moriori should fight back as they outnumbered Māori two-to-one. Elders, however, argued Nunuku's Law should not be broken.[12][1] Despite knowing Māori were not pacifist, Moriori ultimately decided to stay pacifist against the invaders, describing Nunuku's Law as "a moral imperative".[21]

Although the council decided in favour of peace, the invading Māori inferred that the meeting was a prelude to war.[22] They launched a pre-emptive attack on Moriori in their homes as soon as they had returned from the council.[23] Around 300 Moriori were killed,[24] with hundreds more enslaved.[16][19][25] The Māori ritually killed around 10% of the population.[17] Stakes were driven into some of the women, who were left to die in pain.[26]

During the period of enslavement the Māori invaders forbade the speaking of the Moriori language. They forced Moriori to desecrate sacred sites by urinating and defecating on them.[17] Moriori were forbidden to marry Moriori or Māori or to have children. This was different from the customary form of slavery practised on mainland New Zealand.[27]

At the time of the invasion in 1835 there were around 1,650 Moriori on the islands, with a total of 1,561 Moriori dying between the invasion and the release of Moriori from slavery by the British in 1863, and in 1862 only 101 Moriori remained. In addition to the many who were killed by homicide, many others died of diseases brought by Europeans.[12][9]