Knowing what type of writings the Gospels are—for example, legendary versus historical—will help us to understand the writer’s intentions and guide our interpretation. The one method that we have available to assess its type is by looking at its genre, which is an unspoken contract between the writer and the audience on what to expect.
Genre forms a kind of `contract’ or agreement, often unspoken or unwritten, or even unconscious, between an author and a reader, by which the author sets out to write according to a whole set of expectations and conventions, and we agree to read or to interpret the work using the same conventions, giving us an initial idea of what we might expect to find. 
This short piece will explain the various attempts at classifying the Gospels and argues that their genre is akin to that of legendary biographies but not historical ones.
From Folk to Greco-Roman
At one point the Gospels were viewed as being “one of a kind” (sui generis) biographies since the subject lacked personal detail, such as personality, character development, and appearance. In the 1920s, form criticism came to the forefront, and they saw the Gospels as a series of mini-stories but completely void of biographical and historical content.
This led them to conclude that the Gospels were folk literature, that is, pieces of oral tradition passed down and synthesized into narratives. Ben Witherington, on the other hand, a modern New Testament scholar, saw it as the complete opposite:
The whole form critical approach to these Gospels is deeply flawed, for the Gospels do not amount to boiling up narratives from shards and bits of tradition and sayings of Jesus; on the contrary, Gospel writing was a matter of editing the material down in specific ways. 
The modern consensus amongst both secular and non-secular scholars was helped by Richard Burridge, who concludes that the genre of the Gospels should be one of ancient Greco-Roman biography by comparing them to other well established Greco-Roman writings in terms of their form, function, and content.
A prose narrative recounting an individual’s life, often within a chronological framework, employing numerous subgenera (such as sayings, speeches, anecdotes and conflict stories) so as to reflect important aspects of his or her character, principally for purposes of instruction (to inform about what kind of person he or she was), or propaganda (to show his or her superiority to rivals). 
At first glance, this seems to be a fit for the Gospels but upon taking a closer look, we will see that it falls short. The historian Matthew Ferguson, who is a doctoral candidate at the University of California, Irvine, reminds us that fitting the Gospels into a genre isn’t as easy as we may think:
The genre of Graeco-Roman biography was rather diverse in antiquity, with many variations in structure and content depending on the biographical subject being described. As such, the comparison of the NT Gospels with “Graeco-Roman biography” is no simple or straightforward matter, as ancient biographical scholars still debate how the genre can even be defined to begin with.
From Historical to Legendary
Matthew Ferguson concludes that the Gospels are more similar to prose novels and legendary biographies than to historical biographies. This comes from the inference that historical pieces of work were much more analytically rigorous and the focus wasn’t just on the narration of events.
Ancient historical prose has a very distinct style, in which the historian often would discuss the methodology of his research, the sources he consulted, the differences between multiple traditions about a person or event, and his judgment as an inquirer into past affairs. History, derived from the Greek ἱστορία (“inquiry”), is not merely a narrative about past people, places, and events, but is an investigation that one conducts in the present in order to formulate a hypothesis of what probably took place in the past, based on the available evidence. 
In addition, analytical works such as historical biographies, even in times of antiquity, were much more critical towards their subject matter. Novelistic biographies of antiquity include Homer, Alexander the Great, and Aesop, whereas writings by Plutarch, Arrian, and Suetonius are historical biographies. The Gospels show resemblance in broad outline to the biographies of Pythagoras, Empedocles, Asclepius, and, the most uncanny, Apollonius of Tyana which were all about miracle-working “divine men”.
Rather than read as the unmitigated praise of a saint who can do no wrong, ancient historical works and historical biographies were far more critical of their subjects, whom they analyzed less one-dimensionally and more as complete persons. Even for a popular and well-liked emperor like Augustus, his biographer Suetonius in his Life of Augustus still did not hold back from describing Augustus’ acts of adultery and lavish behavior. Good historians are concerned with telling the past as it really is rather than just heaping praise upon individuals as propaganda. 
Gospels as Hagiographies
The Gospels were also written in the third-person by omniscient authors and did not try to chiefly convince us of the accuracy of their accounts but rather that Jesus was heroic and worthy of being our savior. Moreover, all of the Gospels are anonymous, don’t cite their sources or methodologies, and utilize much myth-making, which is atypical of historical biographical material.
Two possible exceptions, one being the Gospel of Luke, where an attempt is made to establish legitimacy since sources were claimed to be passed down to the author. But this passage doesn’t amount to much as it excludes the names of the sources and doesn’t bother to discuss their relevance to the events. The Gospel of John is the other exception where John claims to have an eyewitness disciple but fails to mention a name.
As Morton Smith puts it, these are known as aretalogies because they are “a miracle story or a collection of miracle stories” whose primary purpose was “praise of and propaganda for the deity supposed to have done the deeds.” Below Matthew Ferguson succinctly describes the nature of the Gospels quite well.
The Gospels, in contrast, are not historical biographies but hagiographies written in unquestioning praise of their messianic subject. As a good representation of the scholarly consensus about the aims of the Gospels, the Oxford Annotated Bible (pg. 1744) explains, “Neither the evangelists nor their first readers engaged in historical analysis. Their aim was to confirm Christian faith.” Such works, written for an audience of converts, are not chiefly concerned with being critical or investigative, but rather serve the religious agendas and ideologies of the communities that produced them. 
 Boyd, Gregory A.; Eddy, Paul Rhodes. The Jesus Legend: A Case for the Historical Reliability of the Synoptic Jesus Tradition. Baker Book Group – A.
 Burridge, Richard A. Four Gospels, One Jesus?: A Symbolic Reading.
 Burridge, Richard A. What Are the Gospels?: A Comparison with Graeco-Roman Biography.
 Ehrman, Bart D. The New Testament: A Historical Introduction to the Early Christian Writings.
 Ferguson, Matthew. Κέλσος
 Witherington, Ben. New Testament Rhetoric.