Fully alive to the necessity of restoring discipline and morality at Rome to ensure success without, he at once proceeded to reduce the cost of the papal court after the manner of the Dominican Order to which he belonged, compel residence among the clergy, regulate inns, expel prostitutes, and assert the importance of the ceremonial in general and the liturgy of the Mass in particular. In his wider policy, which was characterized throughout by an effective stringency, the maintenance and increase of the efficacy of the Inquisition and the enforcement of the canons and decrees of the Council of Trent had precedence over other considerations. Accordingly, in order to implement a decision of that council, he standardized the Holy Mass by promulgating the 1570 edition of the Roman Missal. Pope Pius V made this Missal mandatory throughout the Latin rite of the Catholic Church, except where a Mass liturgy dating from before 1370 was in use. This form of the Mass remained essentially unchanged for 400 years until Pope Paul VI's revision of the Roman Missal in 1969/1970, after which it has become widely known as the Tridentine Mass; use of the last pre-1969 edition of the Missal, that by Pope John XXIII in 1962, is permitted without limitation for private celebration of the Mass and is allowed also, under certain conditions, for public use, as laid down in the motu proprio Summorum Pontificum. Some continue to use even earlier editions, but without authorization.
St Pius V recognized attacks on papal supremacy in the Catholic Church and was desirous of limiting their advancement. In France, where his influence was stronger, he took several measures to oppose the Protestant Huguenots. He directed the dismissal of Cardinal Odet de Coligny and seven bishops, nullified the royal edict tolerating the extramural services of the Reformers, introduced the Roman catechism, restored papal discipline, and strenuously opposed all compromise with the Huguenot nobility.
In the list of more important bulls issued by him the famous bull "In Coena Domini" (1568) takes a leading place; but amongst others throwing light on Pope Pius V's character and policy there may be mentioned his prohibition of quaestuary (February 1567 and January 1570); the condemnation of Michael Baius, the heretical Professor of Leuven (1567); the reform of the breviary (July 1568); the denunciation of the "dirum nefas" (August 1568); the banishment of the Jews from the ecclesiastical dominions except Rome and Ancona (1569); the injunction of the use of the reformed missal (July 1570); the confirmation of the privileges of the Society of Crusaders for the protection of the Inquisition (October 1570); the dogmatic certainty of the miraculous conception (November 1570); the suppression of the Fratres Humiliati for profligacy (February 1571); the approbation of the new office of the Blessed Virgin (March 1571); the enforcement of the daily recitation of the canonical hours (September 1571); and the purchase of assistance against the Turks by offers of plenary pardon (March 1572). His response to the so-called reforms of Queen Elizabeth I of England (1558–1603) included support of the imprrisoned Mary, Queen of Scots (1542–67) and her supporters in their attempts to take over England "ex turpissima muliebris libidinis servitute". An important event in the history of Elizabethan England was the publication of a bull, Regnans in Excelsis, dated April 27, 1570, that declared Elizabeth I a heretic and released her subjects from their allegiance to her. This transformed the status of persecuted English Roman Catholics from religious dissidents to potential enemies of the state.
Saint Pius V persistently and successfully attempted to form a general league against the Turks, as the result of which the Battle of Lepanto (October 7, 1571) was won by the combined fleet under Colonna. It is attested in his canonization that he miracously knew when the battle was over, himself being in Rome at the time. Three national synods were held during his pontificate at Naples under Cardinal Alfonso Caraffa (whose family had, after inquiry, been reinstated by Pius V), at Milan under Saint Charles Borromeo, and at Machim.
After his election to the papacy, Pius V continued to wear white, the color of his Dominican habit. Every Pontiff since St Pius V has followed his example of wearing white clothing. Prior to Pope Pius V, Popes, like Cardinals, wore red. This is why some papal accessories, such as the papal shoes, camauro, mozzetta, and cappello romano, are red.
Pius V died on 1 May 1572. He was succeeded by Pope Gregory XIII (1572–85). In 1696, the process of Pius's canonisation was started through the efforts of the Master of the Order of Preachers, Antonin Cloche. He also immediately commissioned a representative tomb from the sculptor Pierre Le Gros the Younger to be erected in the Sistine Chapel of the Basilica di Santa Maria Maggiore. The pope's body was placed in it in 1698. St Pius V was beatified by Pope Clement X in the year 1672, and was later canonized by Pope Clement XI (1700–1721) on 24 May 1712.
In the following year, 1713, his feast day was inserted in the General Roman Calendar, for celebration on 5 May, with the rank of "Double", the equivalent of "Third-Class Feast" in the General Roman Calendar of 1962, and of its present rank of "Memorial". In 1969 the celebration was moved to 30 April, the day before the anniversary of his death (1 May)
The front of his tomb has a lid of gilded bronze which shows a likeness of the dead pope. Most of the time this is left open to allow the veneration of the saint's remains.