He received a doctorate in law and held various positions within the Catholic Church, including Bishop of Camerino and Superintendent of the Papal Exchequer.

The Altieri family belonged to the ancient Roman Papal nobility and had enjoyed the highest consideration at Rome for several centuries; they had occasionally contracted alliances with the Colonnas and the Orsinis.

Pope Urban VIII (1623–44) gave him charge of the works designed to protect the territory of Ravenna from the unruly Po River.

Pope Clement IX (1667–69) named him Superintendent of the Papal Exchequer (in charge of the Church's finances), and in 1667 his maestro di camera, and he was made Secretary of the Congregation of Bishops and Regulars.

The reason a prelate of such transcendent merits received the cardinalate so late in life seems to have been that he had waived his claims to the elevation in favour of an older brother.

He persisted in refusing, protesting that he no longer had strength or memory; eventually, with tears he accepted, and out of gratitude to his benefactor, by ten years his junior, he assumed the name of Clement X.

Occasionally forgetful, he sometimes promised the same favors to different people and came to rely on his cardinal-nephew, Cardinal Paluzzo Paluzzi Altieri degli Albertoni.

The main activity was to invest the Church's money, and with advancing years gradually entrusted to him the management of affairs, to such an extent that the Romans said he had reserved to himself only the episcopal functions of benedicere et sanctificare, resigning in favour of the cardinal the administrative duties of regere et gubernare.

On 12 April 1671, Clement X canonised five new saints: In 1673, he had Pope Leo III's name entered in the Roman Martyrology.

Clement X, on 24 November 1673, beatified nineteen Martyrs of Gorkum, who had been taken prisoner at Gorcum, the Netherlands, and put to death in Brielle on 9 July 1572, in hatred of the Catholic faith, of the primacy of the Pope, and of the Roman Church.

Clement X confirmed the exemptions granted by Pope Gregory XIII (1572–85) to the German College at Rome in 1671; and then, on 16 October 1672, he ordered the pupils to swear that at the close of their studies they would set out for Germany without a day's delay.

Clement X, seeing the results of the apostolic labours of the early French missionaries in Canada, the number of the faithful, and the wide field of labour, resolved to give the Church an independent organisation, and erected a see at Quebec, the bishop to depend directly on the Holy See; this provision would later secure its permanence after Quebec passed into the hands of Great Britain.

At the same time it could not be forgotten that he gave strong financial aid to King John III Sobieski of Poland in their fight against the Turkish invaders.

But Paul Menesius, a Scotsman, who was the ambassador, could not obtain the grant or sanction of that title, though he was received with great magnificence and had many precious gifts to carry back to his master.

The Russian Tsar did not profess the Catholic faith in such a manner as to give any assurance of his intentions, and the King of Poland had looked upon the embassy with displeasure.

Although the government complained that ambassadors had abused their privilege, the diplomatic corps showed discontent that they were not expressly exempted in the new tax law.

Subsequently, the Cardinal nephew wrote to the nuncios who resided in the courts of Europe, stating that the excesses committed by the ambassadors had induced the pope to publish the edict.

Queen Christina of Sweden, who had become a Catholic and moved to Rome in December 1655, made Clement X prohibit the custom of chasing Jews through the streets during the carnival.

[6] Clement X created 20 cardinals in six consistories including Pietro Francesco Orsini, who would become Pope Benedict XIII several decades later.

[1] Pope Clement X had the two fountains located in St. Peter's Square built near the tribune, where a monument has been erected to his memory.