Marcion lived in the second century and was believed to have been the son of the Bishop of Sinope, a city that bordered the Black Sea (Turkey).
His Bishop/father apparently excommunicated Marcion, because of his immorality.
In subsequent years following, Marcion became a wealthy ship owner and moved to Rome around 140 AD.

He became a disciple of the Gnostic heretic, Cerdo, and soon began to establish and promote his own theological doctrines. He was successful in propagating his views and soon attracted a large following throughout the Roman Empire.

At the heart of Marcion's theology was an unscriptural image of God.
Influenced by his Gnostic beliefs, he advocated the doctrine that claimed Jesus was only a mere appearance, a phantom-like figure, and was not in fact born of Mary. That is: Jesus did not come in a physical body. Hence, Marcion rejected the account of the incarnation and humanity of Jesus. The Word, according to Marcion, did not become flesh.

Marcion claimed that Jesus was not the awaited Messiah of the Old Testament, and taught the God of the Old Testament and that of the New Testament were not the same Divine being.
In reading the O.T scriptures, he concluded that the God of Moses and the God of Jesus were completely different entities. Marcion was convinced that the O.T God was a God of harsh justice, arbitrary, inconsistent, tyrannical, prejudicely favored the Jews, and the cause of all evil. Comparatively his New Testament God, who disclosed himself through Jesus, expressed only love and mercy without judgment.

This philosophy proceeded from the Gnostic mindset of mythology originating from Persia. The world, because it was matter, was not made by the one good unknowable God, but by a lesser divinity generated by an emanation (or likeness) of the great Spirit God. This emanation (or demi-urge) which was an evil god, was intent in keeping humanity immersed in ignorance, and was identified as the God of the Old Testament whom they rejected. Hence the spirit God who manifested himself through a spirit-Jesus was non-matter and therefore good. 

To support his doctrine, Marcion formulated his own canon of letters, which rejected the entire Old Testament. His Cannon was based on a revised gospel of Luke (with the account of the nativity removed), and the ten Pauline letters. All other epistles especially those that favored Jewish readers were rejected. This contrast he set forth systematically in his only written work, the "Antitheses", of which only fragments remain. 

According to Marcion the only Apostle that did not corrupt scripture was Paul (and even his epistles were wildly mis-interpreted to suit). He believed that in heaven, Christ sat on the right hand of the Father, and Paul sits on the right hand of Christ, which prompted Tertullian  (father of Latin theology) to write, “Paul had become the apostle of the heretics”.

Such was the threat from Marcionism, which had established Churches of its own, and had grown significantly in numbers to the point of being second only to the Church, that it forced the Church to produce ‘rules of faith’ (creedal declarations of Church doctrine).

The threat of Marcionism impelled people such as Iranaeus to cite and affirm the four gospels – influencing the Church to establish their own Canon; and Tertullian to write about Christian doctrine in defense against the heresy.

This hastened the Church to formally accept the Old Testament alongside the New Testament in its Canon re-affirming that the God of the O.T and the N.T were the same entity, and in doing so, militated against Marcionic doctrine. The Church emphasized Romans 3:25-26 to proclaim God as being just in his forbearance, and (in his love and mercy) the justifier of many, to illustrate the equality of Gods character in “mercy and judgement”. 

The “Gospel of Marcion” was not authored by Marcion himself, but arose later from the sect that followed his teachings. Marcionism flourished in the West and survived until the fifth century in Syria, although traces of it remained in the east into medieval times.  

The error of Marcionic doctrine, however, has continued through the ages and is seen in some cults today that deny the incarnation of Christ, (eg. Jehovah’s Witness and Mormonism); or where a distorted view of God’s love is proclaimed, void of divine attributes of righteous judgement and punishment. (eg. LGCM, -Lesbian Gay Christian Movement) 

Marcionism is unique in while it claimed to follow the ten Pauline letters; it managed to maintain denial of the Lords bodily incarnation and virgin birth all the same. It is a good example of how a powerful movement can rise to such influence by using only selected scripture portions to substantiate its theological belief. Today cults like Bahai and Christian Science follow the same supposition.