In this article, a tripartite interpersonal model is proposed to analyze academic lectures delivered in English. The model combines two approaches to metadiscourse: the reflexive or narrow approach (Mauranen 1993; Ädel 2006), and the interpersonal or broad approach (Hyland 2005, 2019). The criteria adopted by the reflexive approach were exploited to identify metadiscourse in the lectures, whereas the interpersonal approach was drawn upon to ascribe an interpersonal dimension. In associating the two leading approaches, a new interpersonal model has been devised. Using data from the Tunisian Lecture Corpus, the present model is discussed in terms of its distinguishing features and tripartite interpersonal dimensions. It highlights the core features of metadiscourse, which are flexibility and prototypicality, thus offering a more accurate picture of the way the construct operates in the academic lecture genre. This study contributes to situating research on academic lectures within a theory of metadiscourse and to upgrading our current knowledge of metadiscourse. The article concludes by discussing the methodological, theoretical, and pedagogical implications of the proposed model.