The council was convoked by Pope Pius IX on 29 June 1868, under the rising threat of the Kingdom of Italy encroaching on the Papal States.

[1][2] The council's main purpose was to clarify Catholic doctrine in response to the rising influence of the modern philosophical trends of the 19th century.

In the Dogmatic Constitution on the Catholic Faith (Dei Filius), the council condemned what it considered the errors of rationalism, anarchism, communism, socialism, liberalism, materialism, modernism, naturalism, pantheism, and secularism.

[3] Its other concern was the doctrine of the primacy (supremacy) and infallibility of the Bishop of Rome (the Pope),[4] which it defined in the First Dogmatic Constitution on the Church of Christ (Pastor aeternus).

It claimed, as the view of many Catholics in France, that the council would be of very brief duration, since the majority of its members were in agreement, and mentioned inter alia the proclamation of papal infallibility.

[12] From a pragmatic perspective, they feared that defining papal infallibility would alienate some Catholics, create new difficulties for union with non-Catholics, and provoke interference by governments in ecclesiastical affairs.

The draft presented to the council on 8 March drew no serious criticism, but a group of 35 English-speaking bishops, who feared that the opening phrase of the first chapter, "Sancta romana catholica Ecclesia" ('Holy Roman Catholic Church'), might be construed as favouring the Anglican branch theory, later succeeded in having an additional adjective inserted, so that the final text read: "Sancta catholica apostolica romana Ecclesia" ('Holy Catholic Apostolic Roman Church').

[11] The decree did not go forward without controversy; Cardinal Filippo Maria Guidi [it], Archbishop of Bologna, proposed adding that the pope is assisted by "the counsel of the bishops manifesting the tradition of the churches".

The dogmatic constitution states, in chapter 4:9, that the pope has "full and supreme power of jurisdiction over the whole Church" (chapter 3:9); and that, when he:speaks ex cathedra, that is, when, in the exercise of his office as shepherd and teacher of all Christians, in virtue of his supreme apostolic authority, he defines a doctrine concerning faith or morals to be held by the whole Church, he possesses, by the divine assistance promised to him in blessed Peter, that infallibility which the divine Redeemer willed his Church to enjoy in defining doctrine concerning faith or morals.None of the bishops who had argued that proclaiming the definition was inopportune refused to accept it.

With the swift German advance and the capture of Emperor Napoleon III, French troops protecting papal rule in Rome withdrew from the city.

[20] On 20 October 1870, one month after the newly founded Kingdom of Italy had occupied Rome, Pope Pius IX, who then considered himself a prisoner in the Vatican, issued the bull Postquam Dei munere, adjourning the council indefinitely.

[23] In reaction to the political implications of the doctrine of infallibility on the sovereignty of secular states, some of the European kingdoms and republics took rapid action against the Catholic Church.