Of all the claims made in The DaVinci Code, the ones surrounding the veracity and origins of the New Testament are perhaps the easiest to refute, simply because there is such a great amount of authenticated historical evidence that confirms the commonly-accepted understanding of the origin of The Bible.
Rev. Mark D. Roberts offers a good synposis of the way The DaVinci Code portrays the origins of the New Testament:
To begin, let me sketch the picture of the gospels painted in The Da Vinci Code, largely by the historian Sir Leigh Teabing. According to this view, Jesus's life had been "recorded by thousands of followers across the land" (p. 231). In fact, when the Christian canon of Scripture was being identified in the fourth century, according to Teabing, "More than eighty gospels were considered for the New Testament," yet only Matthew, Mark, Luke, and John were chosen, because they fit the political agenda of Constantine (p. 231). (Photo: actor Ian McKellan portraying sir Leigh Teabing in The DaVinci Code.)
Yet among the rejected gospels were many that were "earlier" than the biblical foursome (p. 234). These gospels contained "the original history of Christ" (p. 234), which was rejected by the official Church and embraced only among those labeled as heretics. Even though Constantine and the Church tried to destroy the non-biblical gospels, which Teabing refers to as the "unaltered gospels" (p. 248), some of them did survive.
Of course the "Bible" as we know it today is the product of centuries of debate including a fascinating series of events surrounding the development of the "Old Testament" and its eventual inclusion in the Christian canon. The debate over the Biblican canon continued well into the Protestant reformation; to this day, Protestant Bibles omit several books included in the Old Testament by the Roman Catholic Church.
The New Testament canon familiar to us was first listed by St. Athanasius, Bishop of Alexandria, in 367, in a letter written to his churches in Egypt. That canon gained wider and wider recognition until it was accepted at the Third Council of Carthage in 397, a council of African bishops much under the influence of St. Augustine of Hippo.
But the origins of the New Testament canon go back even further. Around 180 AD, Bishop Iraneus of Lyons recognized the Gospels of Matthew, Mark, Luke, and John, as of divine origin and equivalent to the status of the Hebrew Scriptures. Other contemporaries such as Justin Martyr and Tertullian also emphasized the orthodox nature of Matthew, Mark, Luke, and John, as well as the letters of the Apostle Paul. Another document that surfaced around this time was The Diatessaron, a collection of material from all four orthodox gospels presented as a single document.
In addition, early church writings indicate that each of the major churches not only had copies of the four Gospels, but also copies of the Pauline letters that outlined church doctrine (Romans, I & II Corinthians, Galatians, Ephesians, Philipians, Colossians, etc.) as well as other early orthodox documents such as the Didache, the first and second letters of Clement, and The Shepherd of Hermas. While many early church libraries also had copies of Gnostic writings, by the beginning of the third century AD most of these documents had been discarded by bishops and theologians as being heretical.
Marcion of Sinope also attempted to create a standard scriptural canon for his own church around 150 AD, but his canon did not survive him; Marcion was fond of gnosticism and consequently held a strong disregard for the Hebrew Scriptures. Marcion's canon used portions of Pauline letters and orthodox gospels with references to Hebrew Scripture edited out, and also included a number of works later deemed to be gnostic in origin and therefore heretical.
So it is clear that even though there were perhaps more than a dozen writings -- mostly of Gnostic origin -- claiming to be "gospels," the early church had already determined that Matthew, Mark, Luke, and John were the most reliable and the most likely to have been divinely inspired. There was also widespread agreement on the doctrines that the Apostle Paul spelled out in his various letters. All of ths is well-known and documented; therefore it is
easy to say with great certainty that most of the orthodox New
Testament canon was recognized by the early church long before its bishops met together for the first time in Nicea at the request of Emperor Constantine.