The son of a naval captain, he was actually born aboard a ship in the Baltic Sea where he was brought up by his mother together with his brother until he was five years old. At the age of 15, he joined the French communist party after reading Maxim Gorki's The Mother, a novel which made a lasting impression on him and led him to abandon individualism as he himself recalls in his autobiography From Marx to Christ.
Lepp was an atheist and Marxist for many years and occupied important positions in the communist party with whom he later became very disillusioned. He then converted to Roman Catholicism and was ordained a priest in 1941. He wrote many non-fiction books including some about atheism, religion, and later psychiatry, as he was a psychologist and psychoanalyst.
He wrote among other books: The Psychology of Friendship, The Psychology of Loving, The Authentic Existence, The Communication of Existences. He also wrote Teilhard et la foi des homme, about French thinker Pierre Teilhard de Chardin.
- The Challenges of Life: Viewing Ourselves In Our Existential Totality, 1969
- The Art of Being an Intellectual, 1968
- The Depths of the Soul: a Christian Approach to Psychoanalysis, Staten Island, N.Y.: Alba House, 1966 (orig. Clarté et ténèbres de l’âme: Essai de psychosynthèse, Paris: Aubier, 1956)
- The Ways of Friendship, 1966
- The Authentic Morality, 1965
- A Christian Philosophy of Existence, 1965
- Atheism In Our Time, New York: MacMillan Publishing Co., 1963
- The Psychology of Loving, 1963
- The Christian Failure, 1962
- Hygiene of the Soul (orig. Hygiène De L'Âme, Paris: Aubier, 1958)