In the 2nd century AD Argyll was invaded by Scots (Celts) who came from Ireland, then known as Scotia. The earliest Celtic settlement is assigned to the 3rd century, when a victorious chief, Cairbre Riada, occupied lands in the area later known as Mid Argyll. These lands, called Dalriada, were reinforced from time to time by new bands of immigrants from Celtic Ireland. Dalriada developed gradually as an independent kingdom under ambitious rulers and maintained a separate existence until 843, when one of them, Kenneth I MacAlpin, united the men of Dalriada with the Picts of central Scotland and founded a new hybrid kingdom from which Scotland ultimately emerged. Later, Norsemen obtained control and held sway until 1266, when Argyll was added to the Scottish kingdom. Prior to this, however, semi-independent chiefs of mixed Celtic and Norse ancestry acquired power in Argyll and the Western Isles. One of them, Somerled, really the first lord of the Isles, was killed near Renfrew in 1164 on an expedition against the Scottish king, but the lordship of the Isles was held by his descendants until 1493, when John, the last MacDonald lord of the Isles, was deprived of his vast estates by King James IV. The Campbells of Lochow (now Lochawe) rose on the ruin of the MacDonalds, and their chiefs became earls of Argyll. The combined prominence of the 9 Campbell earls of Argyll in Scottish history and the subsequent 11 dukes of Argyll in the history of Great Britain is perhaps unsurpassed by any other single Scottish family.
The failure of the second Jacobite rising (1745), in which The people of Argyll with few exceptions fought for the Hanoverian George II and against the Stuart pretender, was followed by important political and economic changes. The abolition of the heritable jurisdictions in 1747, prior to which Highland lords and chiefs had been petty kings over their tenants and followers. The rents of tenants became of greater importance to their masters than the former friendly loyalties. Sentimental ties were broken, and the small farms and holdings that had supported large numbers of occupants on a meagre scale of subsistence had to give way to larger farms stocked with flocks of sheep, immediately but only temporarily more profitable to their owners. Throughout the Highlands, including Argyll, thousands of small tenants were displaced."
Religion played an important role. In religious history, St. Columba and
other Celtic Irish missionaries from Iona spread the Gospel throughout the
kingdom of Dalriada in the 6th century. During the first Scottish Reformation
(1560), the 5th Earl of Argyll played a prominent part as the most influential
Protestant layman in Scotland. In subsequent conflicts between Episcopacy and
Presbyterianism, the latter prevailed and is still the most common form of
church government in the Argyll region.