On 30 November 1972, aged 43, he was appointed by Pope Paul VI Bishop of Oran.

[2] Tessier was a member of the Secretariat for relations with non-Christians (1971), as Vice-President of the Arab Caritas International for the country (1975–1987) he was a Muslim-Christian at various symposia and conferences of the two Christians in Palestine involved.

During this period Pierre Claverie, the Bishop of the Roman Catholic Diocese of Oran, was killed and the assassination of the monks of Tibhirine took place.

He was replaced by Father Ghaleb Moussa Abdalla Bader from Latin Patriarchate of Jerusalem.

[5][6] Teissier was nominated on 23 September 2009 by Pope Benedict XVI as a member of the Second Special Assembly of the synod for Africa.