He was believed to have been a student of Rabbi Eliezer of Tarascon. He married a Jewish woman and had children with her. Later, he converted to Christianity and took his children from his wife and made them Christians. He then joined the Dominican Order. Prior to the 1263 Disputation of Barcelona, he was known for following Nicholas Donin's lead in attempting to ban the Talmud. His arguments centered on the "irrational" material within the text. His participation in the Disputation of Barcelona with Nahmanides was to try his new missionary technique to bring Jews to Christianity.
The failure in the Disputation did not, however, discourage Christiani. Provided through the agency of Raymond de Penyafort with letters of protection from King James I of Aragon, he went on missionary journeys, compelling the Jews everywhere to listen to his speeches and to answer his questions, either in their synagogues or wherever else he pleased. They were even required to defray the expenses of his mission.
In spite of the protection granted him by the king, Christiani did not meet with the success he had expected; he therefore went to Pope Clement IV and denounced the Talmud, asserting that it contained passages derogatory to Jesus and Mary. The pope issued a bill (1264) to the Bishop of Tarragona, commanding him to submit all the copies of the Talmud to the examination of the Dominicans and Franciscans. A commission was then appointed by the king, Christiani being one of its members, to act as censors of the Talmud; and they obliterated all passages which seemed to them to be hostile to Christianity. In 1269 Christiani interceded with King Louis IX of France and obtained from him the enforcement of the canonical edict requiring Jews to wear badges.
- Kobak, Joseph Jeschurun p. 21
- Lattes, Isaac "Kiryat Sefer" in Medieval Hebrew Chronicles II p. 238
- Kobak, Joseph Jeschurun pp. 21–22
- Kobak, Joseph Jeschurun, pp. 1–15