Is Catholicism the original branch of Christianity?

(Yes. CHRISTianity started with Jesus Christ. Christ started only one church. He chose 12 apostles. These were the first priests of the Catholic faith. Jesus even appointed Peter to act as the first Pope of his church here on earth. Jesus said that His church would prevail for all time until His return. Jesus loved His church and referred to it in parable as his "bride". Showing us that He would take care of it, love it and nourish it as a groom would do for His wife.

Catholicism is the only original faith started by Jesus Christ. All other forms of Christianity have been created by men.

Other forms of Christianity have branched off from Catholicism. Such as Protestant during the Reformation of Martin Luther. Then even other religions have branched off from Protestant, like Lutheranism, etc...)

Catholic Answer

Roman is an epithet first commonly used in England after the protestant revolt to describe the Catholic Church. It is never used by the Catholic Church. No, Catholicism is not a branch of Christianity, it is the ONLY form of Christianity. The protestants and other "separated brethern" who are validly baptised are considered Christians but the eccesliasl communities to which they belong are NOT considered "branches" of Christianity. Jesus Christ quite plainly stated that He established His Church on Peter, and that It would remain ONE under the guidance of the Holy Spirit until the end of the world. That Church, by the way, is composed of sinners, even priests; because, although the Church, itself, is holy, Jesus established It to call sinners, and everyone of It's members is, by definition, a sinner, and will be until we are perfected and enter heaven.

from A Catholic Dictionary, edited by Donald Attwater, Second edition, revised 1957

Christian

A name first given to the followers of our Lord at Antioch (Acts xi, 26). Since the rise of Protestantism the name has been used in so many different senses as to have become almost meaningless: it may indicate a Catholic or a Unitarian, or even be applied to an infidel who displays some virtue which is associated with Christ. It may reasonably be applied to the members of all the ancient churches, whether in communion with the Holy See, or not, and to those Protestants who profess, explicitly or implicitly, the Nicaean creed in its traditional interpretation. The Church puts no definite official meaning on the word, as she does on Catholic.

Christianity is the religion of, the body of faith and morals taught by, the Catholic Church of Christ. The word may be properly extended to include the religious systems of the dissident Eastern -churches and of some Protestant bodies. The current popular use of the word in an ethical, subjective sense, is to be deplored: it is stripping it of all objective or historical connotations.

Catholic I. The word is derived from Greek and simply means universal. In combination with the word "church" it essentially merely indicates one of the marks of the Church, and was so used by St. Ignatius at the beginning of the 2nd century; but in the course of history it has come to be the distinguishing epithet of the Church of Christ and his faith: under other circumstances its place might have been taken by "apostolic" or "one." The use of the word in this distinguishing way became current and common in England only from the middle of the 16th century. In some mediaeval translations of the Creed unam sanctam catholicam et apostolicam ecclesiam is rendered "one holy apostolic church general."

ii. A Catholic is any person who, having been baptized, does not adhere to a non-Catholic religion or perform any act with the intention or effect of excluding himself from the Church. A "good Catholic" is one who practises his religion to the best of his ability.

iii. Catholics normally call themselves Catholics without qualification, and are distinguished by the name alike in West and East; except for a body of High Anglicans, no other Christians use the name as a distinguishing title. But Catholics of the Byzantine rite sometimes calls themselves Greek Catholics, Chaldeans are so called, and Maronites always refer to themselves simply as Maronites - they avoid the name Catholic for the good reason that there is no such thing as a Maronite who is not a Catholic, and because in Syria the epithet particularly designates a Catholic Melkite.

iv. As an adjective, Catholic in this special sense should only be used of subjects of which Catholicity is predicable, e.g., a man as man, a church, building, or catechism. To speak of a Catholic artist or grocer, Catholic poetry or truth is inaccurate and misleading: an artist or grocer who is a Catholic is a Catholic as a man (and this without reference to whether he paints only ecclesiastical pictures or supplies cheese only to the clergy); poetry may deal with a Catholic theme or be written by a poet who is a Catholic, but is not by that fact anything but poetry; truth is truth and it is improper to call the truth about the Catholic Church, Catholic truth; (cf., Catholic arithmetic, a Wesleyan judge, Quaker music, and, particularly, Catholic culture).

from The Catechism of the Catholic Church, second edition, English translation 1994

II. The Church is Holy.

823 "The Church . . . is held, as a matter of faith, to be unfailing holy. This is because Christ, the Son of God, who with the Father and the Spirit is hailed as 'alone holy,' loved the Church as his Bride, giving himself up for her so as to sanctify her; je joined her to himself as his body and endowed her with the gift of the Holy Spirit for the glory of God." (Lumen Gentium 39; cf. Eph 5:25-26.) The Church, then, is "the holy People of God," (Lumen Gentium 12.) And her members are called "saints." (Acts 9:13; 1 Cor 6:1; 16:1).

824 United with Christ, the church is sanctified by him, through him and with him she becomes sanctifying. "All the activities of the Church are direct, as toward their end, to the sanctification of men in Christ and the glorification of God." (Sacrasanctum concilium10) It is in the Church that "the fullness of the means of salvation" (Unitatis redintegratio 3 § 5) has been deposited. It is in her that "by the grace of God we acquire holiness." (Lumen Gentium 48)

825 "the church on earth is endowed already with a sanctity that is real though imperfect." (Lumen Gentium 48 § 3) In her members perfect holiness is something yet to be acquired: "Strengthened by so many and such great means of salvation, all the faithful, whatever their condition or state-though each in his own way-are called by the Lord to that perfection of sanctity by which the Father himself is perfect."(Lumen Gentium 11 § 3)

826 Charity is the soul of the holiness to which all are called: it "governs, shapes, and perfects all the means of sanctification." (Lumen Gentium 42).

If the Church was a body composed of different members, it couldn't lack the noblest of all; it must have a Heart, and a Heart BURNING WITH LOVE. And I realized that this love alone was the true motive force which enabled the other members of the Church to act; if it ceased to function, the Apostles would forget to preach the gospel, the Martyrs would refuse to shed their blood. LOVE, IN FACT, IS THE VOCATION WHICH INCLUDES ALL OTHERS; IT'S A UNIVERSE OF ITS OWN, COMPRISING ALL TIME AND SPACE-IT'S ETERNAL! (St. Therese of Lisieux, Autobiography of a Saint, tr. Ronald Knox {London: Harvill, 1958})

827 "Christ, 'holy, innocent, and undefiled,' knew nothing of sin, but came only to expiate the sins of the people. The Church, however, clasping sinners to her bosom, at once holy and always in need of purification, follows constantly the path of penance and renewal." (Lumen Gentium 8 § 3; cf. Unitatis redintegratio 3; 6; Heb 2:17; 7:36; 2 Cor 5:21) All members of the Church, including her ministers, must acknowledge that they are sinners. (Cf. 1 Jn 1:8-10) In everyone, the weeds of sin will still be mixed with the good wheat of the Gospel until the end of time. (Cf. Mt 13:24-30) Hence the Church gathers sinners already caught up in Christ's salvation but still on the way to holiness:

The Church is therefore holy, though having sinners in her midst, because she herself has no other life but the life of grace. If they live her life, her members are sanctified; if they move away from her life, they fall into sins and disorders that prevent the radiation of her sanctity. This is why she suffers and does penance for those offenses, of which she has the power to free her children through the blood of Christ and the gift of the Holy Spirit. (Paul VI, Solemn Profession of Faith: Credo of the People of God)

No, it is not a branch of Christianity, it IS Christianity and the original Christian Church.