Thomas is believed to have been born in the castle of Roccasecca in the old county of the Kingdom of Sicily, which is now known as the Lazio region of Italy, in 1225. His parents were well-off, but as the youngest son Thomas was expected to enter the monastery.
At 5-years-old, Thomas began his education at Monte Cassino, where he remained until the military conflict between Emperor Frederick II and Pope Gregory IX reached the abbey. He was then transferred and enrolled at the studium generale in Naples.
It is believed that Thomas was introduced to his philosophical influences – Aristotle, Averroes, and Maimonides – at the university, where he also met John of St. Julian, a Dominican preacher, who influenced him to join the recently founded Dominican Order.
When Thomas’ family learned of his decision, his mother Theodora arranged for him to be moved to Paris. When Thomas was travelling to Rome, his brothers captured him and returned him to their parents at the castle of Monte San Giovanni Campano.
Thomas was held captive in the castle for one year as his family tried to keep him from joining the Dominican Order. In the year he was held, Thomas tutored his sisters and communicated with members of the Dominican Order.
In an effort to change Thomas’ mind, two of his brothers hired a prostitute to seduce him, but legends claim Thomas drove her off with a fire iron. That night, two angels appeared to him in a dream and strengthened his resolve to remain celibate.
When Theodora realized she could not sway her son, she tried to preserve the family name by arranging for his escape through a window. She believed a secret escape was better than appearing to accept his decision.
Following his escape in 1244, Thomas turned to Naples, then to Rome and met the Master General of the Dominical Order, Johannes von Wildeshausen.
The next year, Thomas went to study at the Faculty of the Arts at the University of Paris, where he is believed to have met Dominican scholar Albertus Mangus, the Chair of Theology at the College of St. James.
In 1248, Thomas chose to follow Mangus to the new studium generale at Cologne rather than accepting Pope Innocent IV’s offer to appoint him abbot of Monte Cassino as a Dominican. Though Thomas hesitated, when they reached the university, Mangus appointed him magister studentium.
Thomas was quiet and seldom spoke at the university, leading other students to believe he was mentally delayed, but Mangus prophetically said, “You call him the dumb ox, but in his teaching he will one day produce such a bellowing that it will be heard throughout the world.”
Following the conclusion of his education, Thomas taught in Cologne as an apprentice professor and instructed students on the books of the Old Testament. It was during this time he wrote Expositio super Isaiam ad litteram, Postilla super Ieremiam, and Postilla super Threnos.
In 1252, Thomas returned to Paris to earn his master’s degree in theology. As an apprentice professor, he lectured on the Bible and devoted his final three years of his education to Peter Lombard’s Sentences.
Thomas composed a commentary on Sentences, titled Scriptum super libros Sententiarium and also wrote De ente et essentia.
The spring of 1256 saw Thomas appointed regent master in theology at Paris, and one of his first works after assuming the office was Contra impugnantes Dei cultum et religionem, in defense of mendicant orders, which William of Saint-Amour had been attacking.
Between 1256 to 1259, Thomas spent his tenure writing several books, such as Questiones disputatae de veritate, Quaestiones quodlibetales, Expositio super librum Boethii De trinitate, and Expositio super librum Boethii De hebdomadibus. At the conclusion of his regency, Thomas was in the process of writing one of his most famous works, Summa contra Gentiles.
In 1259, Thomas completed his first regency and returned to Naples, where he was appointed general preacher. In September 1261, he was asked to lecture in Orvieto, and during his stay he finished Summa contra Gentiles, as well as Catena aurea, and Contra errores graecorum.