As a cardinal he was independent of the factions in the papal court, and he opposed the election of Celestine. Boniface was elected on Celestine's abdication, and during his first years he was opposed by those who had suffered from Celestine's retirement—the Neapolitans, the Colonna family, and the extreme Franciscans, among them Jacopone da Todi. To preclude schism, Boniface kept Celestine imprisoned for the rest of his life. Boniface reigned in a time of crisis in Europe. He wished to emulate St. Gregory VII and Innocent III, but he was no such statesman, and the times had changed. He interfered in Sicily, but he was openly flouted when Frederick II and the Sicilians forced Boniface to recognize Frederick as king. He brought Charles of Valois into Italy to pacify Florence and succeeded only in stirring up more trouble. Dante was exiled in this struggle of Guelphs and Ghibellines.
Boniface's contest with Philip IV of France was the principal feature of his career. The pope tried to stop Philip from his illegal levies on the clergy by the bull Clericis laicos (1296), enunciating the principle that laymen could not tax clerics without the consent of the Holy See. Philip retaliated by cutting off the contributions of the French church to Rome. In England the Pope faced an equally resistant Edward I, and in a subsequent bull (1297) Boniface relaxed the ruling. The dispute began again in earnest in 1301 with the trial of Bernard Saisset, and Boniface never again yielded.
Two of his statements in the controversy are famous—the bull Ausculta fili (1301), which summoned a French synod to meet at Rome to discuss the reformation of French affairs, and the bull Unam sanctam (1302), an extreme statement (not naming Philip) of the principle that Catholic princes as well as others are subject to the pope in temporal (moral) and religious matters. Philip paid no attention, and in 1303 he sent Nogaret to Italy, soon proclaiming his intention of deposing the pope. Nogaret found the pope at Anagni and harassed him; the pope stood firm and according to tradition was slapped by Nogaret's companion, Sciarra Colonna. The outraged people of Anagni thereupon drove out the soldiery; Boniface was rescued and escorted to Rome. He died in a month.
Philip pursued Boniface dead as he had alive. In 1310 he forced Clement V to begin a process to determine that Boniface was heretical; that accusation was abandoned, but Clement consented to repudiate such of Boniface's acts as had hurt Philip. Boniface, an excellent canon lawyer, planned and promulgated a substantial addition to the existing law, called the Sext (1298) since it was the sixth book added to the five-volume compilation of Gregory IX. He was the first to establish (1300) a holy year. He was succeeded by Benedict XI.
See C. T. Wood, Philip the Fair and Boniface VIII: State vs. Papacy (1967).
In 1264, Benedict became part of the Roman Curia where he served as secretary to Cardinal Simon of Brie on a mission to France. Similarly, he accompanied Cardinal Ottobono Fieschi to England (1265-1268) in order to suppress a rebellion by a group of barons against Henry III, a churchman in England. Upon Benedict's return from England, there is an eight year period in which nothing is known about what occurred in his life. After this eight year period of uncertainty, Benedict was sent to France to supervise the collection of a tithe in 1276 and then became a papal notary in the late 1270s. During this time, Benedict accumulated seventeen benefices which he was permitted to keep when he was promoted, first to cardinal deacon in 1281 and then 10 years later as cardinal priest. As cardinal, he often served as papal legate in diplomatic negotiations with France, Naples, Sicily, and Aragon.
He was elected in December 24, 1294 after Pope Celestine V abdicated in December 13. There is a legend that it was Boniface VIII's doing that Celestine V renounced the papacy - for Boniface, previously Benedetto, convinced Celestine V that no person on the earth could go through life without sin. However, in later times, it is a more common understanding that Celestine V resigned by his own designs and Benedetto merely showed that it was allowed by Church law. Either way, Celestine V left and Boniface VIII took his place as pope. One of his first acts as pontiff was to imprison his predecessor in the Castle of Fumone in Ferentino, where he died at the age of 81, attended by two monks of his order. In 1300, Boniface VIII formalized the jubilees, which afterwards became a source of both profit and scandal to the church. Boniface VIII founded the University of Rome La Sapienza in 1303.
Boniface VIII put forward some of the strongest claims to temporal, as well as spiritual, supremacy of any Pope and constantly involved himself with foreign affairs. In his Bull of 1302, Unam Sanctam, Boniface VIII proclaimed that it "is absolutely necessary for salvation that every human creature be subject to the Roman pontiff", pushing papal supremacy to its historical extreme. These views and his intervention in "temporal" affairs led to many bitter quarrels with the Emperor Albert I of Habsburg (1291-1298), the powerful family of the Colonnas, with Philip IV of France (1285–1314) and with Dante Alighieri (who wrote De Monarchia to argue against it).
After complications involving the capture of Jean Lemoine by Philip, the conflict was re-ignited. In December of 1301, Philip was sent the Papal Bull Ausculta fili ("Listen, My Son"), informing Philip that "God has set popes over kings and kingdoms."
The feud between the two reached its peak in the early 14th century when Philip began to launch a strong anti-papal campaign against Boniface. On November 18, 1302, Boniface issued one of the most important papal bulls of Catholic History: Unam Sanctum. It declared that both spiritual and temporal power were under the pope's jurisdiction, and that kings were subordinate to the power of the Church.
In response, Guillaume de Nogaret, Philip's chief minister, denounced Boniface as a heretical criminal to the French clergy. In 1303, Philip and Nogaret were excommunicated. However, on September 7, 1303 an army led by Nogaret and Sciarra Colonna of the Colonna family surprised Boniface at his retreat in Anagni. The King and the Colonnas demanded that he resign, to which Boniface VIII responded that he would "sooner die". Boniface was beaten badly and nearly executed but was released from captivity after three days. He died a month later, on October 11, 1303.
After the humiliating ordeal of Boniface, no popes would ever again challenge or seriously threaten kings and emperors despite further excommunications and interdictions. In the future, the Church would see itself becoming subordinate to the growing power of the European nation-states and their secular leaders, and the church's secular power would forever be lost. It is also interesting to note that this was the first event that marked the downfall of the Church's prestige, and the decline of its prestige and advertisement of its corruptions led to the Reformation.
Boniface VIII was buried in St. Peter's Basilica in a grandiose tomb that he had designed himself. (Allegedly, when the tomb cracked open three centuries after his death (on October 9, 1605), his body was revealed to be perfectly incorrupt.)
The historicity of these testimonies is disputed among scholars. T. Boase, whose 1933 biography of Pope Boniface VIII is often regarded as still the best, comes to the conclusion, "The evidence is not unconvincing ... but it was too late, long years after the event, to construct an openly held heresy out of a few chance remarks with some newly-added venom in construing them" (361).
The posthumous trial against the memory of Boniface VIII was in any case settled without a result in 1311.