Born to impoverished Italian nobility, the son of Paolo Ghislieri and Domenica Augeria. Worked as a shepherd as a boy. Received an excellent training in piety and holiness, including a scholastic education from a Dominican friar; he joined the Order himself in 1518, taking the name Michele. Studied in Bologna, Italy. Ordained in 1528 in the diocese of Genoa, Italy. Teacher of philosophy and divinity in Genoa. Professor of theology in Pavia, Italy for sixteen years. Master of novices and prior of several Dominican houses, working for stricter adherence to the Order’s Rule. Inquisitor in Como and Bergamo, Italy. Commissary general of the Roman Inquisition in 1551. On 4 September 1556 Michele was consecrated Bishop of Nepi e Sutri, Italy against his will. Inquisitor in Milan and Lombardy in 1556. Created cardinal on 15 March 1557. Grand inquisitor on 14 December 1558. Part of the conclave of 1559 that elected Pope Pius IV. Bishop of Mondovi, Italy on 17 March 1560. As bishop, Michael worked to lead his flock with words and examples, and served as a continual messenger encouraging personal piety and devotion to God. Chosen 225th pope in 1566.
Upon his ascension to the papacy, Pius V immediately faced the task of enacting the reforms of the Council of Trent. New seminaries were opened, a new breviary, new missal, and new catechism were published; foundations were established to spread the Faith and preserve the doctrine of the Church. Pius spent much time personally working with the needy. He built hospitals and used the papal treasury to care for the poor. Pius faced many difficulties in the public forum, both in the implementation of the Tridentine reforms and in interaction with other heads of state. At the time of his death he was working on a Christian European alliance to break the power of the Islamic states.