It was the largest, most populous and wealthiest diocese of the medieval Scottish Catholic church, with territory in eastern Scotland stretching from Berwickshire and the Anglo-Scottish border to Aberdeenshire.

It came to be one of two archdioceses of the Scottish church, from the early 16th century having the bishoprics of Aberdeen, Brechin, Caithness, Dunblane, Dunkeld, Moray, Orkney and Ross as suffragans.

[1] The obituary of Túathalán, the abbot in question, constitutes the earliest literary evidence for St Andrews.

[7] Because Scotland, north of the Forth, had never been in the Roman Empire or part of Anglo-Saxon England, it was difficult for the church of York to produce any evidence of its claim, but it was established that Britannia had two archbishops in the Latin hierarchy.

Requests were made to the papacy for an archbishopric at St Andrews, and although these failed, the Scottish bishoprics were recognised as independent in 1192.

[4] The diocese was the largest in the medieval Kingdom of Scotland territorially, stretching from Berwick-upon-Tweed to Nigg on the river Dee near Aberdeen.

[13] The bishops possessed a castle in St Andrews, and manors through their diocese fortified during the episcopate of William de Lamberton: Inchmurdo, Dairsie, Monimail, Torry, Kettins and Monymusk, all north of the Forth, and Stow of Wedale, Lasswade, and Liston in Lothian.