[2] On Trinity Sunday 1835, Pope Gregory XVI created the Vicariate Apostolic of Western Oceania,[3] splitting it from the territory entrusted to the Congregation of the Sacred Hearts of Jesus and Mary {Picpus Fathers} as the area had proven too large.

On 29 April 1836, he formally approved the "Priests of the Society of Mary" or Marist Fathers as a religious institute and assigned to it the mission of Western Oceania.

Pompallier, who had been closely associated with the Marists, was named Vicar Apostolic, and consecrated Titular Bishop of Maronea on 30 June 1836.

They arrived in early January at the Canary Islands, where Father Claude Bret caught a fever and died at sea some two months later.

Europa stopped at Mangareva in the Gambier Islands on 13 September where Pompallier met Bishop Rouchouze, Vicar Apostolic for Eastern Oceania.

They left Tahiti on 23 October on the schooner Raiatea to drop off Father Pierre Bataillon and Brother Joseph-Xavier at Wallis, the main seat of the mission in Tonga.

A woman by the Kalisi Tuipulotu hid the men in her house until it was safe enough to continued their journey to Futuna, arriving on 8 November 1837.

There Chanel, a French lay brother Marie-Nizier Delorme, and an English Protestant layman named Thomas Boag, who had been resident on the island and had joined them at Tonga seeking passage to Futuna, left the group.

On 30 December Pompallier, Fr Louis Catherin Servant SM and Brother Michel (Antoine) Colombon sailed for the Hokianga and arrived at the home of Thomas and Mary Poynton on 10 January 1838.

Bishop Pompallier travelled extensively by schooner around both North and South Islands, setting up mission stations.

[1] By 1843, he had established stations in Hokianga, Kororāreka, Mangakahia, Kaipara, Tauranga, Akaroa, Matamata, Ōpōtiki, Maketu, Auckland, Otago, Wellington, Ōtaki, Rotorua, Rangiaowhia and Whakatāne.

[6] Marist reinforcements arrived on the Reine de Paix on 18 June 1839 (Fathers Baty, Jean-Baptiste Épalle [fr] and Petit and Brothers Elie Regis, Augustin and Florentin).

Fifty years later, in his 1890 publication about the Treaty, William Colenso recorded that Pompellier arrived dressed in full "canonicals" (ceremonial robes) and did not appear at ease.

Nevertheless, mainly due to Pompellier's insistence on the matter of religious tolerance, Henry Williams said to those present "E mea ana te Kawana, ko nga whakapono katoa, o Ingarani, o nga Weteriana, o Roma, me te ritenga Maori hoki, e tiakina ngatahitia e ia."

Difficulties arose between Marist superior Jean-Claude Colin, in Lyon, and Bishop Pompallier over jurisdiction and finances.

The vicariate was divided into the Dioceses of Auckland (covering the northern half of the North Island) and Wellington (the rest of New Zealand).

They became his loyal lieutenants and good friends and especially assisted Pompallier as diocesan administrators and in attending to the Māori mission.