Which books of the New Testament were written by a gentile?

A:Apart from Paul, a Jew, we can not be certain of any of the other New Testament authors. However most, if not all, were gentiles.

The four New Testament gospels are attributed to Matthew, Mark, Luke and John, with Luke a gentile, but these attributions only took place later in the second century. New Testament scholars have demonstrated that the gospels attributed to Matthew, Luke and John were largely based on the gospel attributed to Mark, and say that they could not have been written by the persons to which they are attributed. We also know all the New Testament gospels were written in Greek Koine, the language of the gentiles, and as far as can be established they were actually written by gentiles.

Just as John's Gospel was certainly not written by the apostle John and was likely written by a gentile living in the Johannine community, so also the three Epistles of John were probably written by gentiles.

Because it is signed by a person called John, the Book of Revelation was once also attributed to the apostle John, but scholars say that this work was entirely unrelated to the other books that came to be attributed to the apostle John. To avoid confusion, the author of Revelation is now properly called John of Patmos, and he was probably a gentile.

Another Answer:

Luke is commonly noted as the only Gentile writer of a New Testament book. It is from Colossians 4:10-14 that this seems to be the case (differentiates first circumcised then others):

Colossians 4:10-14New King James Version (NKJV)

10 Aristarchus my fellow prisoner greets you, with Mark the cousin of Barnabas (about whom you received instructions: if he comes to you, welcome him), 11 and Jesus who is called Justus. These are my only fellow workers for the kingdom of God who are of the circumcision; they have proved to be a comfort to me.

12 Epaphras, who is one of you, a bondservant of Christ, greets you, always laboring fervently for you in prayers, that you may stand perfect and complete in all the will of God. 13 For I bear him witness that he has a great zeal for you, and those who are in Laodicea, and those in Hierapolis. 14Luke the beloved physician and Demas greet you.

As a companion of Paul and a highly educated man who clearly was not present during Jesus' ministry. Tradition and early Christian writings of Justin Martyr to Tertullian, identify Luke as the author of the Gospel of Luke.