The book is technically an anonymous work, as are all of the gospels. In no part of the original text is the author identified. So how do we know who wrote the book that we know as "the Gospel according to Mark"? To answer that question we have to turn to the history of the early church for it not only has preserved the text of the book, but also the history about the book. While the records and documents that we have from the early church are valuable, it is worth stating up front that they are not Scripture and they are not free from error.
The early church is unanimous in claiming that the author of the book is Mark, who served alongside Peter and recorded the things that he taught. The earliest such testimony is found in the writings of Papias. He wrote 5 books that were called Expositions of Oracles of the Lord (circa 110). These books are no longer extant, but they were available to Irenaeus (180) and Eusebius (325) the latter having preserved most of what we have today in his Church Histories.
Papias was a bishop of Hierapolis (in Asia Minor near Colossae and Laodicea). According to Eusebius, who had access to his full works, stated that Papias heard much of his information second hand from those who studied under the apostles.
But Papias himself in the preface to his discourses by no means declares that he was himself a hearer and eye-witness of the holy apostles, but he shows by the words which he uses that he received the doctrines of the faith from those who were their friends. ... And Papias, of whom we are now speaking, confesses that he received the words of the apostles from those that followed them, but says that he was himself a hearer of Aristion and the presbyter John. At least he mentions them frequently by name, and gives their traditions in his writings. These things we hope, have not been uselessly adduced by us.(Eccl Hist 3.39.2,7)There is some debate today as to whether Papias himself was a student of the Apostle John or an elder named John. It is the elder John (possibly the Apostle John) who passed on to Papias the earliest information we have about the author of the gospel.
"This also the presbyter said: Mark, having become the interpreter of Peter, wrote down accurately, though not in order, whatsoever he remembered of the things said or done by Christ. For he neither heard the Lord nor followed him, but afterward, as I said, he followed Peter, who adapted his teaching to the needs of his hearers, but with no intention of giving a connected account of the Lord’s discourses, so that Mark committed no error while he thus wrote some things as he remembered them. For he was careful of one thing, not to omit any of the things which he had heard, and not to state any of them falsely.” These things are related by Papias concerning Mark. (Eccl Hist 3.39.15)From this passage we learn the following:
- Mark was the author, recording what Peter preached.
- Mark was not a disciple of Jesus (while Jesus was alive).
- Mark wrote his account without error.