Francis was born in 1567 in the castle of Sales, diocese of Geneva, to Francis, Count of Sales, and Frances of Sionas.
From his earliest years he showed a marked inclination for goodness and great docility.

He did his first studies at Annecy, and from there was sent to Paris. Here he studied rhetoric, philosophy and theology with the Jesuit Fathers. His life was withdrawn: he attended church and the sacraments; from that time he made a vow of chastity.

Having completed his studies in Paris, his father sent him to Padua to study law. There Francis was exposed to great dangers, which he escaped happily with his strong will and the help of God in whom he always trusted.

Francis' father had thought of making his son one of the most esteemed gentlemen in society and had already obtained for him a distinguished position in the senate of Chambery, while he was preparing a rich party for him. Francis, however, was called to something else, and he disclosed everything to his tutor, instructing him to make his father aware of it. His parents opposed many obstacles, but seeing him firm in his purpose, they consented to the will of God.

When he was made a priest, the Bishop of Geneva entrusted him with the task of fighting the heresy of Calvin, which infested the whole of Chiablese. Many refused to listen to him, so Francis wrote leaflets and posters, with concise and precise instructions on the Catholic Faith, which he posted on the walls and ran under the doors of the houses, which remained closed to his knocking. Our Saint had to work and suffer a lot for those heretics, and he was in danger of being assassinated several times, but his great gentleness, united to a tireless zeal and an exemplary piety, won over the most obstinate Calvinists so much so that he converted, they say, 72 thousand. When Bishop Granier of Geneva died, Francis was elected to succeed him.

In 1610 he founded the order of the Sisters of the Visitation, together with St. Jeanne Frances de Chantal. When he felt that he no longer had the strength he once had and that his health was failing, he asked for help in governing the diocese. Although he was ill, he climbed the pulpit in Lyons for the last time on the eve of Holy Christmas 1622, but the next day he had to take to his bed, with obvious signs of progressive apoplexy. He immediately asked for the last Sacraments, then with seraphic fervor he repeated some passages of the Holy Scripture, until the illness took away his speech and life, on the evening of December 28. He was not yet 56 years old, 20 of which were spent in the episcopate.

He is famous for his incomparable sweetness, he wrote two important works: the Filotea or Introduction to the devout life and the Teotimo or Treatise on the love of God. Two works of very high spirituality and at the same time very concrete and affordable to anyone who wanted to live deeply the Christian life in everyday life.

He is invoked as the patron saint of journalists and deaf-mutes.