The 1980s saw an explosion of scholarly work on the ‘Arian controversy’, which sought to rethink the categories of the controversy ab initio. Building on this, a number of figures connected with the controversy came in for individual study in the 1990s, including the bishop Marcellus of Ancyra, who was the subject of a number of books and articles in that decade, nearly all of which concentrated on his theology and touched his place in the historical events of the wider controversy only tangentially. This thesis attempts to situate Marcellus in relation to the major ecclesiastical events of the controversy between 314 and 345, arguing that attention to his role gives a better picture of how the ‘anti-Arian’ party in particular understood itself during these years. Marcellus’ skills as administrator and canonist, displayed in the 314 Synod of Ancyra, over which he presided, form the background to the portrayal of him that emerges. His roles before and during the synod of Nicaea, before, during and after the synods of Tyre and Jerusalem, in Rome for fifteen months during the years 339-341, and at the synod of Sardica are examined, and furnish a number of new suggestions for ways to understand these events. The synod of Ancyra which was moved by Constantine to Nicaea, it is suggested, was not originally called by the emperor, but by Alexander and his allies, with the express purpose of condemning Eusebius of Nicomedia and his allies, with Marcellus as the intended president. Gerhard Feige’s view that Marcellus was doubtless, like Eustathius of Antioch, unhappy with the actual synod of Nicaea, and contrary to popular assumption had little to do with the writing of the creed (which he did not even personally sign), is endorsed, although Marcellus’ greater involvement in the writing of the canons is suggested. The synod of Tyre is shown by careful examination of the various accounts of it, particularly that of Eusebius of Caesarea, to have been a travesty, a view which builds on Girardet’s analysis of its views of its own authority in relation to the canonical traditions of the time. Marcellus’ role in the creation of the myth of ‘Arianism’ is examined, a myth which is shown to have taken its characteristic form in Rome during the period he and Athanasius spent there together.