St Fidelis subsequently taught philosophy at the University of Freiburg, ultimately earning a "doctor of laws". During his time as a student he did not drink wine, and wore a hair-shirt. He was known for his modesty, meekness, and chastity.
In 1604, he accompanied three young gentlemen of Switzerland on their travels through the principal parts of Europe. During six years of travel, he attended Mass very frequently; in every town where he came, he visited the hospitals and churches, passed several hours on his knees in the presence of the Blessed Sacrament, and gave to the poor sometimes the very clothes off his back.
Upon his return to Switzerland, he practiced law as a counsellor or advocate, at Colmar, in Alsace. He scrupulously forbore all invectives, detractions, and whatever might affect the reputation of any adversary. His charity procured him the surname of "counsellor and advocate for the poor". Disenchanted with the evils associated with his profession, he was determined to enter the Capuchin friars.
The Calvinists of that territory, being incensed at this attempt to convert their brethren, loudly threatened Fidelis' life, and he prepared himself for martyrdom. Ralph de Salis, and another Calvinist gentleman, were both converted by his first conferences. Fidelis and his companions entered into Pretigout, a small district of the Grisons, in 1622, on the "Feast of the Epiphany" (January 6). The effects of his ardent zeal, where the Bishop of Coire sent a lengthy and full account to the Congregation for the Propagation of the Faith, enraged the Calvinists in that province.
On April 24, 1622, St Fidelis made his sacramental confession, said Mass, and then preached at Grüsch. At the end of his sermon, which he had delivered with more than ordinary zeal, he stood silent all of a sudden, with his eyes fixed upon Heaven, in ecstasy. He foretold his death to several persons in the most clearest terms, and began signing his letters, "P. Fidelis, prope diem esca vermium" ("Father Fidelis, in days ahead to become food for worms").
A local account:
From Grüsch he went to preach at Sévis, where, with great energy, he exhorted the Catholics to constancy in the faith. After a Calvinist had discharged his musket at him in the Church, the Catholics entreated him to leave the place. He answered that death was his gain and his joy, and that he was ready to lay down his life in God's cause. On his road back to Grüsch, he met twenty Calvinist soldiers with a minister at their head. They called him a false prophet, and urged him to embrace their sect. He answered: "I am sent to you to confute, not to embrace your heresy. The Catholic religion is the faith of all ages, I fear not death." One of them beat him down to the ground by a stroke on the head with his backsword. Fidelis rose again on his knees, and stretching forth his arms in the form of a cross, said with a feeble voice "Pardon my enemies, O Lord: blinded by passion they know not what they do. Lord Jesus, have mercy on me. Mary, Mother of God, succor me!." Another sword stroke clove his skull, and he fell to the ground and lay in a pool of his own blood. The soldiers, not content with this, added many stab wounds to his body with their long knives, and hacked-off his left leg, as they said, to punish him for his many journeys into those parts to preach to them.
After six months, the martyr's body was found to be incorrupt, but his head and left arm were separated from his body. The body parts were then placed into two reliquaries, one sent to the Cathedral of Coire, at the behest of the bishop, and laid under the High Altar; the other was placed in the Capuchin's Convent Church of Weltkirchen, Feldkirch, Austria.