[5] The nineteenth century historian William F. Skene wrote that during the reign of Robert I (r.1306–1329), the Mac Cailinmor branch (descendants of Colin Mor Campbell) did not possess any land in what is now Argyll, while Mac Arthur, head of the Mac Arthur branch was in possession of extensive territory in the earldom Garmoran, which was the original seat of the Campbells.

[5] Skene wrote that "it is therefore impossible to doubt that Mac Arthur was at this time the head of the clan, and this position he appears to have maintained until the reign of James I of Scotland.

"[5] Arthur Campbell, of the Mac Arthur branch, along with Neil Campbell, of the Mac Cailinmor branch, supported Robert the Bruce and were richly rewarded by the king with the forfeited lands of his opponents.

[5] Arthur Campbell was made keeper of Dunstaffnage Castle along with extensive territory in the district of Lorne.

[5] Later, during the reign of David II, the Mac Cailinmor ever becoming more powerful, since the marriage of Sir Neil Campbell with a sister of Robert I, were resisted from taking control of the clan by the Mac Arthur branch with the obtaining of a charter "Arthuro Campbell quod nulli subjictur pro terris nisi regi," by Arthur Campbell.

["Arthur Campbell that he is subject to no one for the lands but the king"][5] In 1427 James I held parliament at Inverness and summoned the Highland chiefs.

[1][5] From this time, and on, the Mac Cailinmor branch were the head of the clan and the Campbells continued their rise in power.

[5] In 1771 Patrick MacArthur, chief of Clan Arthur, died in Jamaica without a male heir.

In 1986 senior members of Clan Arthur hired a genealogist to trace back through the last chief's family tree to find a living representative with a common ancestor to the chiefs of Clan Arthur.

The blazon of the chief's armorial shield is Azure, three antique crowns Or and corresponds to one of the attributed arms of the legendary King Arthur.