Guillaume Courtet, OP (1589–1637) was a French Dominican priest who has been described as the first Frenchman to have visited Japan.^[1][2] He was martyred in 1637 and canonized in 1987.^[3]

Courtet was born in Sérignan, near Béziers, in 1589 or 1590. He entered the orders in the city of Béziers and later entered the Dominicans in Toulouse.

Courtet was active in the diplomatic field during the Thirty Years' War and was remarked by the French statesman Richelieu.^[4]

In 1636, Guillaume Courtet entered Japan in secret, with the objective of furthering Western efforts to promote Christianity there. He was accompanied by a Spanish friend named Miguel de Ozaraza.

Entering Japan was a very dangerous endeavour, as Christianity had been prohibited in the country since 1613. Courtet entered the country under the Spanish name Tomaso de Santo Domingo.^[4] He sailed from the Philippines and disembarked in Ishigaki-jima, but a few days later he was caught and imprisoned for one year. From there he was brought to Kagoshima and then Nagasaki.^[5]

In an attempt to make him apostatize, he was tortured by being submitted to the "torture of the water", the "torture of the alênes" (needles under the fingernails) and the hanging torture of tsurushi.^[6] He remained true to his faith, however, and as a result he was beheaded with his friends on 29 September 1637.^[4]

The Positio Super Introductione Causae or the cause of beatification was authored by respected historian, Fidel Villarroel, which led to his beatification during Pope John Paul II's papal visit to the Philippines.^[7][8][9] It was the first beatification ceremony to be held outside the Vatican in history.

Guillaume Courtet became a saint on 18 October 1987 among the 16 Martyrs of Japan.

• France-Japan relations