Born at Chanonat in the diocese of Clermont, France, on 17 May 1811, Jean Pezant, later known as Jean Étienne Pezant, was the son of a farmer, Michel Pezant, and his wife, Marie. He studied at the seminary of St Sulpice in Paris and became a curate at Romagnat, Clermont, before joining the Society of Mary in 1839. After training at Lyons, he made his profession in January 1840 and sailed the following month in the corvette L'Aube for the Bay of Islands, to work as a Marist missionary in New Zealand.
Arriving in New Zealand on 11 July 1840, Pezant sailed almost immediately for Akaroa, where he was stationed until November. He then accompanied Bishop J. B. F. Pompallier to Otago Harbour, Wellington and Mahia. In March 1841 Pompallier left him to take over the Tauranga mission, and from there Pezant travelled extensively in the North Island, reaching as far as North Taranaki. In 1844 he was sent to Matamata, moving his headquarters to Rangiaowhia. This station became the most successful of the Catholic Maori missions: between 1844 and April 1850 Pezant recorded 1,042 baptisms and 198 marriages.
When the Marists moved to the diocese of Wellington in 1850, Father Pezant moved with them. He was sent twice to visit Taranaki, in September 1850 and April 1851, and in the second half of 1851 was stationed at Otaki. In February 1852 he became the first parish priest in Wanganui, with oversight of the Taranaki area, and continued to do missionary work among the coastal tribes between the Patea and Rangitikei rivers. In 1853 Governor George Grey granted land for a parish church in Wanganui. Pezant designed an imposing building, and had it built with the help of soldiers of the 18th and 65th regiments. On 15 August 1857 Bishop P. J. Viard blessed it; it was dedicated under the name 'The Sacred Heart of Mary'. During the same visit Viard blessed the Chapel of the Holy Angels at Ruakopiha, the centre of Pezant's mission work in the Waitotara Valley. Pezant blessed his third church, at Turakina, on 20 September 1858. At Rangitikei his work among Ngati Apa was based at Onepuehu. The Pai Marire movement ended mission work, however, and when government troops entered South Taranaki in 1865, Pezant provided them with a map made during his journeys between New Plymouth and Wanganui, and ministered to the soldiers in the field.
In July 1868 Pezant was moved to the South Island, where he became assistant to Father Augustin Sauzeau, parish priest at Blenheim. In 1871, when Picton and the Marlborough Sounds became a separate parish, he was appointed its first parish priest. He was a well-known figure, and was often seen walking round his parish. In 1880 ill health forced his retirement to Blenheim; he died on 22 December at Riverlands, south of Blenheim. He was buried at Picton.
One of the pioneer Catholic missionaries in the colony, Pezant, who signed his name John Stephen Pezant on documents in New Zealand, was regarded as 'one of the best Maori scholars in New Zealand' and was successful in his missions among the Maori. Unlike some of his confrères he was not a controversial figure, but he did not shrink from expressing his views within the church; for instance, opposing Pompallier's decision not to use Maori transliterations of biblical names if formulated by Protestants. Pezant was successful in making the transition from missionary to parish priest. He was a notable builder of churches, regardless of debt accrued, and gave no thought to his own comfort. His parish work won universal respect, even from Protestant ministers.