He is the son of Arnaud de Lassus, chief engineer of the maritime industry, member of Cité catholique, and founder of Action Family and School and has six brothers, one of whom became a Carmelite in the convent of Créteil, with the name of Sister Aude of the Virgin Mary.
Michel de Lassus entered the Charterhouse at the age of 20 and took the name of Dysmas, in reference of Penitent thief of the Gospel.
Dysmas de Lassus become the 74th successor of Saint Bruno at the head of the Carthusian Order, succeeding Dom François-Marie Valut, who resigned for health reasons.
He participated in the writing of Cardinal Robert Sarah's book, The Force of Silence, Against the Dictatorship of Noise, written with Nicolas Diat, and published in October 2016.
[3] In March 2020, at éditions du Cerf, he published "Risques et dérives de la vie religieuse", offering diagnostic elements that will help measure the dangers of certain spiritual practices or the governance of religious communities.