He founded the Congregation of the Most Holy Redeemer (the Redemptorists). In 1762 he was appointed Bishop of Sant'Agata dei Goti. A prolific writer, he published nine editions of his Moral Theology in his lifetime, in addition to other devotional and ascetic works and letters. Among his best known works are The Glories of Mary and The Way of the Cross, the latter still used in parishes during Lenten devotions.
He was born in Marianella, near Naples, then part of the Kingdom of Naples, on 27 September 1696. He was the eldest of eight children of Giuseppe and Anna Cavalieri Liguori. Two days after he was born, he was baptized at the Church of Our Lady the Virgin as Alphonsus Mary Anthony John Cosmas Damian Michael Gaspard de' Liguori. The family was of noble and ancient lineage, but the branch to which the Saint belonged had become somewhat impoverished. Alphonsus's father, Don Joseph de' Liguori, was a naval officer and Captain of the Royal Galleys. His mother was of Spanish descent.
Liguori learned to ride and fence but was never a good shot because of poor eyesight. Myopia and chronic asthma precluded a military career so his father had him educated for the legal profession. He was taught by tutors before entering the University of Naples, where he graduated with doctorates in civil and canon law at 16. He remarked later that he was so small at the time that he was almost buried in his doctor's gown and that all the spectators laughed. When he was 18, like many other nobles, he joined the Confraternity of Our Lady of Mercy with whom he assisted in the care of the sick at the hospital for "incurables".
He became a successful lawyer. He was thinking of leaving the profession and wrote to someone, "My friend, our profession is too full of difficulties and dangers; we lead an unhappy life and run risk of dying an unhappy death". At 27, after having lost an important case, the first he had lost in eight years of practicing law, he made a firm resolution to leave the profession of law. Moreover, he heard an interior voice saying: "Leave the world, and give yourself to me."