The Immaculate Conception was formally declared as a dogma of the faith by Bl. Pope Pius IX in 1854 by a Solemn Definition with his document “Ineffabilis Deus“. Some people have gotten the idea that this came out of the blue, as it were, and elevated an old dispute into an article of faith, or created the liturgical celebration of it. This is actually not the case.
In the first place, the liturgical feast of the Immaculate Conception predated Bl. Pius IX for quite some time. It was already present in the Breviary and Missal, although some of the texts were changed when Pius IX promulgated the doctrine. The feast was instituted in the west very early, in the 700s, and persisted for some years. It is often said that everyone was against it until Bl. Duns Scotus argued for it in the 14th century, and after that it became more common. This is also false. What you had with the Immaculate Conception was a “Period of Doubt”, wherein, beginning with St. Bernard, some theologians began to question this teaching, and positively deny it in favor of the teaching that Our Lady was sanctified in the womb.
These doubts were based upon the consequences that appeared to result from it, namely, that it would mean she wouldn’t need Christ as savior, or, the scriptural reference “All have sinned”. Nevertheless, all of these were first answered by St. Bonaventure, who predicated how the doctrine could in fact be true, although he did not accept it, favoring instead the teaching of his master, Alexander of Hales. This doctrine was taught and held in the Church. There was never a “consensus” opposed to it, and it was finally confirmed by the Church’s Solemn Magisterium.
Cardinal Franzelin, a peritus at Vatican I, also notes the state of this doctrine prior to Pius IX’s solemn judgment. When marking the distinction between “Divine Tradition” and “Ecclesiastical Tradition”, he remarks: “For at present , all Catholics believe the Immaculate Conception of the Blessed Virgin Mary is Divine Tradition; yet before it was certainly established through the definition of the Supreme Pontiff on this Tradition, for a long time, all the theologians and faithful who were asserting this doctrine, understood that it must be asserted by no other means than divine tradition. Others reasonably did not doubt it was from Tradition, but what kind it might have been, whether divine, or merely apostolic or ecclesiastical; but nothing appeared to be, or certainly, was not sufficiently evident for them on this [tradition].”1
Now there is another point that is more commonly debated. The Tradition of the Immaculate Conception originated not in the West but in the East (which ultimately is the origin of our faith). Yet the Eastern Orthodox, both the Greek and non Greek Rites, both Chalcedonian and non-Chalcedonian dispute this doctrine, claiming it is a novelty and against their tradition.
Therefore I am linking a well researched paper which clearly shows their tradition that the Orthodox Tradition does in fact support the doctrine of the Immaculate Conception. It becomes clear, when studying this issue, that the Orthodox teaching is really just an eccleisological reaction to the fact of a “Solemn Judgment”, which their theology denies as a prerogative of the Pope, holding that only a Council has that authority. One of the nice things about this paper, is that it cuts through a normal error of western apologists who try to make this case, who render to a saying like “most pure, all Immaculate” in their liturgy or amongst this or that Father as evidence of the Immacualte Conception, when in reality, that doesn’t necessarily follow in Greek. This paper, by Fr. Gillet, focuses on actual propositions which clearly teach that. You can read it here: The Immaculate Conception and Orthodoxy
1 “Sic nunc omnes Catholici divinam credunt Traditionem immaculatum conceptum beatissimae Virginis; antequam autem de hac Traditione per definitionem Summi Pontificis certo constaret, omnes jam theologi et fideles, qui eam doctrinam asserebant, non ex alia quam ex divina Traditione asserendam esse intelligebant: contra alii non sane de traditione, qualis esset an divina an mere apostolica aut ecclesiastica dubitabant; sed nulla esse vel certe non satis de ea constare illis videbatur.” De Divina Traditione, 1875, Rome, Thesis I, pg. 17.