The title, "According to John," indicates John wrote John. There are some Church Fathers that ascribe the text to John the Apostle. Attestation of Johannine authorship is evidenced as early as Irenaeus. Eusebius wrote that Irenaeus received his information from Polycarp, who is said to have known the apostles.

John 21.20–25 contains information that is autobiographical. The first person "I" in verse 25, the disciple in verse 24 and the disciple whom Jesus loved (also known as the Beloved Disciple) in verse 20 are the same person. Critics concede the abrupt shift from third person to first person in vss. 24–25 indicates that the author of the epilogue is the Apostle John.

An early document from circa 170, the Muratorian fragment, states that John was the primary author.