In my online article on Acts, I conclude that "Acts stands out as a work of ancient history." The genre of Luke, however, can be somewhat more elusive. The preface and literary relationship with Acts count strongly in favor of classifying it as ancient history, but the focus on Jesus and other features, such as the recounting of his lineage, are clear biographical elements. David Aune classifies Luke as ancient historiography for the aforementioned reasons and his inclination to keep their genre unified. Craig Keener, on the other hand, see no problem in classifying Luke as biography and Acts as history. Further, no assessment would be complete without recounting Richard Burridge's analysis of the Synoptics, including Luke, and his conclusion that they all fall within the genre of biography.
Although acknowledging the strong biographical focus on Luke, I lean towards classifying it as ancient historiography. As I explained in an early CADRE post, "Acts is the second volume of a two-volume literary effort, not just a sequel." Luke was written , "with the writing of Acts specifically in mind," with the author saving some scenes for Acts and setting the plate for Acts to address issues set up in Luke. The preface of Luke, therefore, was intended to introduce the clearly historiographical Acts as well as Luke. As I recount in my Acts article, the preface strongly relates to historiographical writings of the era.
What tips the balance for me, however, is a particular phrase in the preface, Luke:1-4:
Many have undertaken to draw up an account of the things that have been fulfilled among us, just as they were handed down to us by those who from the first were eyewitnesses and servants of the word. Therefore, since I myself have carefully investigated everything from the beginning, it seemed good also to me to write an orderly account for you, most excellent Theophilus, so that you may know the certainty of the things you have been taught.By distinguishing his own work with others on the same issue, Luke explicitly signals his intent to write about history. It is not an "account of the life of Jesus," but "things" that have been "fulfilled among us." The account, in other words, is not just about the life of Jesus but has a broader scope encompassing the Christian movement. As Aune notes, the phrase "'the events completed among us,' the subject of Luke's composition, indicates a historical rather than biographical focus, even though (following Hellenistic historical practice) prominent personalities dominate both books." Davide Aune, The New Testament in its Literary Environment, page 121.
Writing about the scholars who see Luke's Gospel as exemplifying the "formal characteristics" of Hellenistic historiography, Bridget Feign notes, "The most striking of them is the prologue (Luke1:1-4), which echoes both the structure and language of similar prologues by such recognized historians as Herodotus, Thucydides, Polybius, and especially, Josephus. Aune (1987: 121) points out that the phrase "events fulfilled among us" in the prologue (Luke 1:3) suggests a focus on events-the subject of historiography-even though prominent personalities dominate both books." Brigid Curtin Frein, "Genre and Point of View in Luke's Gospel," Biblical Theology Bulletin, Vol. 38, page 5.
The choice of terms -- focusing on events rather than on a person -- should not be passed over lightly, as happenstance or unintentional. Prologues such as the one found in Luke were carefully crafted. Luke chose to broaden his subject despite the strong focus on Jesus in Luke (and Peter and Paul in Acts, for that matter). He did so to signal that he was writing a history of significant events, one that soon thereafter include a second volume, rather than a biography. This does not detract from clear biographical elements in Luke's Gospel. Nor does it deny that a study and comparison of ancient biography is a useful point of inquiry for understanding Luke's Gospel. It merely means that the author of Luke primarily intended to have his Gospel understood as a part of a broader history. That broader history was centralized around Jesus, but his impact and influence went far beyond living a significant life.