The study of Jesus in comparative mythology is the examination of the narratives of the life of Jesus in the Christian gospels, traditions and theology, as they relate to Christianity and other religions. Although the vast majority of New Testament scholars and historians of the ancient Near East agree that Jesus existed as a historical figure, most secular historians also agree that the gospels contain large quantities of ahistorical legendary details mixed in with historical information about Jesus's life. The Synoptic Gospels of Mark, Matthew, and Luke are heavily shaped by Jewish tradition, with the Gospel of Matthew deliberately portraying Jesus as a "new Moses". Although it is highly unlikely that the authors of the Synoptic Gospels directly based any of their accounts on pagan mythology, it is possible that they may have subtly shaped their accounts of Jesus's healing miracles to resemble familiar Greek stories about miracles associated with Asclepius, the god of healing and medicine. The birth narratives of Matthew and Luke are usually seen by secular historians as legends designed to fulfil expectations about the Messiah.

The Gospel of John bears some influences from Platonism, and may also have been influenced in less obvious ways by the cult of Dionysus, the Greek god of wine, though this possibility is still disputed. Later Christian traditions about Jesus were probably influenced by Greco-Roman religion and mythology. Much of Jesus's traditional iconography is apparently derived from Mediterranean deities such as Hermes, Asclepius, Serapis, and Zeus and his traditional birthdate on 25 December, which was not declared as such until the fifth century, was at one point named a holiday in honour of the Roman sun god Sol Invictus. At around the same time Christianity was expanding in the second and third centuries, the Mithraic Cult was also flourishing. Though the relationship between the two religions is still under dispute, Christian apologists at the time noted similarities between them, which some scholars have taken as evidence of borrowing, but which are more likely a result of shared cultural environment. More general comparisons have also been made between the accounts about Jesus's birth and resurrection and stories of other divine or heroic figures from across the Mediterranean world, including "dying-and-rising gods" such as Tammuz, Adonis, Attis, and Osiris, although the concept of "dying-and-rising gods" itself has received scholarly criticism.

Early apologists like Justin Martyr and Tertullian, attributed the supposed ritualistic parallels with Christianity to demons of the past who foresaw the coming Christ. Pagan rituals in traditional Greco-Roman religions which resembled the sacraments, were considered counterfeits from the devil. They would too make comparisons with Jesus and the sons of Zeus, likely to defend Christian practice from persecution. Similar to Origen, they also argued that there were "seeds of truth" in pagan religions and philosophy, and thus partial revelations. Critics like Celsus accused Christian beliefs of being built on fables, and highlighted the virgin birth of Jesus. He saw it as analogous to the many miraculous conception stories of Greek heroes born from gods and mortals.

The majority of New Testament scholars and historians of the ancient Near East agree that Jesus existed as an historical figure. While some scholars have criticized Jesus scholarship for religious bias and lack of methodological soundness, with very few exceptions such critics generally do support the historicity of Jesus and reject the Christ myth theory that Jesus never existed. There is widespread disagreement among scholars about the accuracy of details of Jesus's life as it is described in the gospel narratives, and on the meaning of his teachings, and the only two events subject to "almost universal assent" are that Jesus was baptized by John the Baptist and that he was crucified under the orders of the Roman prefect Pontius Pilate. It is also generally, although not universally, accepted that Jesus was a Galilean Jew who called disciples and whose activities were confined to Galilee and Judea, that he had a controversy in the Temple, and that, after his crucifixion, his ministry was continued by a group of his disciples, several of whom were persecuted.

Nonetheless, most secular scholars generally agree that the gospels contain large amounts of material that is not historically accurate and is better categorized as legend. In a discussion of genuinely legendary episodes from the gospels, New Testament scholar Bart Ehrman mentions the birth narratives in the Gospels of Matthew and Luke and the release of Barabbas. He points out, however, that, just because these accounts are not true does not mean that Jesus himself did not exist. According to theologians Paul R. Eddy and Gregory A. Boyd, there is no evidence that the portrayal of Jesus in the Synoptic Gospels (the three earliest gospels of Mark, Matthew, and Luke) was directly influenced by pagan mythology in any significant way. The earliest followers of Jesus were devout Jews who abhorred paganism and would have therefore been extremely unlikely to model accounts about their founder on pagan myths.

Despite this, several scholars have noticed that some of the healing miracles of Jesus recorded in the Synoptic Gospels bear similarities to Greek stories of miracles associated with Asclepius, the god of healing and medicine. Brennan R. Hill states that Jesus's miracles are, for the most part, clearly told in the context of the Jewish belief in the healing power of Yahweh, but notes that the authors of the Synoptic Gospels may have subtly borrowed from Greek literary models. He states that Jesus's healing miracles chiefly differ from those of Asclepius by the fact that Jesus's are attributed to a human being on earth; whereas Asclepius's miracles are performed by a distant god. According to classical historians Emma J. Edelstein and Ludwig Edelstein, the most obvious difference between Jesus and Asclepius is that Jesus extended his healing to "sinners and publicans"; whereas Asclepius, as a god, refused to heal those who were ritually impure and confined his healing solely to those who thought pure thoughts. Scholars disagree whether the parable of the rich man and Lazarus recorded in Luke 16:19–31 originates with Jesus or if it is a later Christian invention, but the story bears strong resemblances to various folktales told throughout the Near East.

It is, however, widely agreed that the portrayal of Jesus in the gospels is deeply influenced by Jewish tradition. According to E. P. Sanders, a leading scholar on the historical Jesus, the Synoptic Gospels contain many episodes in which Jesus's described actions clearly emulate those of the prophets in the Hebrew Bible. Sanders states that, in some of these cases, it is impossible to know for certain whether these parallels originate from the historical Jesus himself having deliberately imitated the Hebrew prophets, or from later Christians inventing mythological stories in order to portray Jesus as one of them, but, in many other instances, the parallels are clearly the work of the gospel-writers. The author of the Gospel of Matthew in particular intentionally seeks to portray Jesus as a "new Moses". Matthew's account of Herod's attempt to kill the infant Jesus, Jesus's family's flight into Egypt, and their subsequent return to Judaea is a mythical narrative based on the account of the Exodus in the Torah. In the Gospel of Matthew, Jesus delivers his first public sermon on a mountain in imitation of the giving of the Law of Moses atop Mount Sinai. According to New Testament scholars Gerd Theissen and Annette Merz, the teachings preserved in the sermon are statements that Jesus himself really said on different occasions that were originally recorded without context, but the author of the Gospel of Matthew compiled them into an organized lecture and invented context for them in order to fit his portrayal of Jesus as a "new Moses".

According to Sanders, the birth narratives in Matthew and Luke are the clearest examples of legends in the Synoptic Gospels. Both accounts have Jesus born in Bethlehem, in accordance with Jewish salvation history, and both have him growing up in Nazareth, but they present two different explanations for how that happened. The accounts of the Annunciation of Jesus's conception found in Matthew 1:18–22 and Luke 1:26–38 are both modelled on the accounts of the annunciations of Ishmael, Isaac, and Samson in the Old Testament. Matthew quotes from the Septuagint translation of Isaiah 7:14 to support his account of the virgin birth of Jesus. The Hebrew text of this verse states "Behold, the young woman [ha'almāh] is with child and about to bear a son and she will call him Immanuel." The Septuagint, however, translates the Hebrew word 'almāh, which literally means "young woman", as the Greek word παρθένος (parthenos), which means "virgin". Most secular historians therefore generally see the two separate accounts of the virgin birth from the Gospels of Matthew and Luke as independent legendary inventions designed to fulfill the mistranslated passage from Isaiah. Sanders clarifies that the birth narratives are "an extreme case" resulting from the gospel authors' lack of knowledge about Jesus's birth and childhood; no other part of the gospels relies so heavily on Old Testament parallels. Sanders also notes that, despite the clearly intentional parallels, the "striking differences" between Jesus and the prophets of the Old Testament are also highly significant and the gospels' accounts of Jesus's life on the whole do not closely resemble the lives of any of the figures in the Hebrew Bible.