For a time he was canon at the church of Santa Maria Maggiore, then he became Camerlengo of the Holy Roman Church in January 1188 and Cardinal Deacon of Santa Lucia in Silice on February 20, 1193. Under Pope Clement III (1187–91) and Pope Celestine III (1191–98) he was treasurer of the Roman Church, notably compiling the Liber Censuum. Acting Vice-Chancellor of the Holy Roman Church 1194 until 1198.
On July 18, 1216, all cardinals present at the death of Innocent III assembled at Perugia (where Innocent III had died two days previously) with the purpose of electing a new Pope. The troubled state of affairs in Italy, the threatening attitude of the Tatars, and the fear of a schism induced the cardinals to agree to an election by compromise. Cardinals Ugolino of Ostia (afterwards Pope Gregory IX) and Guido of Praeneste were empowered to appoint the new Pope. Their choice fell upon Cencio Camerario, who accepted the tiara with reluctance and took the name of Honorius III. He was consecrated at Perugia on July 24th, was crowned at Rome 31 August, and took possession of the Lateran 3 September 1216. The Roman people were greatly elated at the election, for Honorius III was himself a Roman and by his extreme kindness had endeared himself to the hearts of all.
Like his famous predecessor Innocent III, he set his mind on the achievement of two great things, the recovery of the Holy Land in the Fifth Crusade and a spiritual reform of the entire Church; but quite in contrast with Innocent III he sought these achievements by kindness and indulgence rather than by force and severity.
The Fifth Crusade was endorsed by the Lateran Council of 1215, and he started preparations for the crusade to begin in 1217. To procure the means necessary for this colossal undertaking, the Pope and the cardinals were to contribute the tenth part, and all other ecclesiastics the twentieth part, of their income for three years. Though the money thus collected was considerable, it was by no means sufficient for a general crusade as planned by Honorius III.
Far-reaching prospects seemed to open before him when he crowned Pierre de Courtenay (April, 1217) as Latin Emperor (1217–18) of Constantinople; but the new Emperor was captured on his eastward journey and died in confinement.
Honorius III was aware that there was only one man in Europe who could bring about the recovery of the Holy Land, and that man was his former pupil Frederick II (1212–50) of Germany. Like many other rulers, Frederick II had taken an oath to embark for the Holy Land in 1217. But Frederick II hung back, and Honorius III repeatedly put off the date for the beginning of the expedition.
Most rulers of Europe were engaged in wars of their own and could not leave their countries for any length of time. Andrew II of Hungary (1205–35) and, somewhat later, a fleet of crusaders from the region along the Lower Rhine finally departed for the Holy Land, took Damietta and a few other places in Egypt; but lack of unity among the Christians, also rivalry between the leaders and the papal legate Pelagius, resulted in failure.
June 24, 1225, was finally fixed as the date for the departure of Frederick II; and Honorius III brought about his marriage with Isabella, heiress of the Kingdom of Jerusalem, with a view to binding him closer to the plan. But the Treaty of San Germano in July 1225 permitted a further delay of two years.
Frederick II now made serious preparations for the crusade. In the midst of it, however, Pope Honorius III died in Rome on March 18, 1227 without seeing the achievement of his hopes. It was left to his successor, Pope Gregory IX (1227–41), to insist upon their accomplishment.
But Honorius III really had too large a task; besides the liberation of the Holy Land, he felt bound to forward the repression of Cathar heresy in the south of France, the war for the faith in the Spanish peninsula, the planting of Christianity in the lands along the Baltic Sea, and the maintenance of the impossible Latin empire in Constantinople.
Of these duties the rooting out of heresy lay nearest to Honorius III's heart. In the south of France he carried on Innocent III's work, confirming Simon de Montfort in the possession of the lands of Raymond VI of Toulouse and succeeding, as Innocent III had not, in drawing the royal house of France into the conflict.
The most widely important event of this period was the siege and capture of Avignon. Both Honorius III and Louis VIII of France (1223–26) turned a deaf ear to Frederick II's assertion of the claims of the empire to that town.
Honorius III gave papal sanction to the Dominican order in 1216, and to the Franciscan in 1223. He approved the Rule of St. Dominic in his Bull Religiosam vitam, dated December 22, 1216, and that of St. Francis in his Bull Solet annuere, dated November 29, 1223.
During his pontificate also many of the tertiary orders first came into existence. He approved in 1221 the Franciscan Brothers and Sisters of Penance Rule with the Bull Memoriale Propositi. On January 30, 1226, he approved the Carmelite Order in his Bull Ut vivendi normam. He also approved the religious congregation "Val des Ecoliers" (Vallis scholarium, Valley of scholars), which had been founded by four pious professors of theology at the University of Paris.
Being a man of learning, Honorius III insisted that the clergy should receive a thorough training, especially in theology. In the case of a certain Hugh whom the chapter of Chartres had elected bishop, he withheld his approbation because the bishop-elect did not possess sufficient knowledge, quum pateretur in litteratura defectum, as the Pope states in a letter dated January 8, 1219. Another bishop he even deprived of his office on account of illiteracy.
He bestowed various privileges upon the universities of Paris and Bologna, the two greatest seats of learning during those times. In order to facilitate the study of theology in dioceses that were distant from the great centres of learning, he ordered in his Bull Super specula Domini that some talented young men should be sent to a recognized theological school to study theology with the purpose of teaching it afterwards in their own dioceses.
Honorius III acquired some fame as an author. The most important of his writings is the Liber censuum Romanae ecclesiae, which is the most valuable source for the medieval position of the Church in regard to property, and also serves in part as a continuation of the Liber Pontificalis. It comprises a list of the revenues of the Apostolic See, a record of donations received, privileges granted, and contracts made with cities and rulers. It was begun under Clement III and completed in 1192 under Celestine III. The original manuscript of the Liber Censuum is still in existence (Vaticanus latinus 8486).
Honorius III wrote also a life of Celestine III; a life of Gregory VII; an "Ordo Romanus", which is a sort of ceremonial containing the rites of the Church for various occasions; and thirty-four sermons.
The attribution of a grimoire (spell book) to the Pope is of unknown authenticity as to its authorage.