In 1923 Tournier received an M.D. degree at the University of Geneva. During his student years he acted as the Swiss President of the student movement Zofingia and became a Red Cross delegate for the repatriation of Austrian and Russian prisoners of war in Vienna.

Through 1924 Tournier was assistant medical Doctor at the Medical Polyclinic in Geneva under Prof. Bickel. In 1925 Tournier opened a private practice in Geneva and started operating as general medical practitioner.

Tournier became increasingly interested in Calvinism and the Reformed faith, and was heavily involved in civic and medical groups. In 1932 he joined the Oxford Group. As a result of his interests he investigated the relationship between Medicine, counseling, and spiritual values. Although he initially considered giving up Medicine for counseling, he finally decided to combine the two, and in 1937 he transformed his private medical practice into a counseling practice.

This encounter caused him to radically change his medical practice. Instead of merely treating the physical disorders of his patients, he started addressing the deeper problems of the whole person. In 1937 he wrote a letter to all his patients informing them of this new orientation.

In 1940 he published his first book Médecine de la Personne (trans. The Healing of Persons), which was dedicated to Frank Buchman, the founder of the Oxford Group, wherein he advocates that man is more than just body and a mind, he is also a spiritual being. This combination is what makes man a person. Therefore, it is impossible to know and treat him if one disregards his deepest reality. After the success of Médecine de la Personne he became a prolific Writer of books dealing with the subject. Although he did not have any formal training in psychiatry or theology, his writing has influenced a generation of medical and religious professionals the world over. His books would eventually be translated into thirteen languages.

Around 1946 he disassociated himself from the Oxford Group (now called Moral Re-Armament). He would eventually (in 1982) reconcile with the group (renamed again as Initiatives of Change).

Psychosomatic Medicine was still in its infancy, and Tournier observed that the contemporary approach to illness was purely organic and failed to consider the patient as a whole. Tournier saw the need to consider not only the physical aspects of health, but also the psychological and spiritual dimensions. He therefore invited medical colleagues from a variety of fields and a number of Philosophers to reflect on this with him. 1947 marked the first meeting of this international study group called Médecine de La Personne, and which has met annually ever since. According to the group:

Two religious experiences would underlie Tournier’s later work. When he was 12, he became a Christian. As he grew up he became active in the church, started writing articles about Calvinism, and argued for orthodoxy and against liberalism. His Christian experience did not, however, become totally meaningful to him until a second experience, which he called a “face-to-face encounter with God”. This encounter transformed his life and changed everything, and gave him a vital interest in “that other side of life, for its inner dimension, so necessary to us."