In the Annals of the Four Masters it is stated that "Somerled, son of Gilbrigid, king of Innsie Gall " (i.e., the Sudreys), died in 1083. The Norwegian name of Somerled, which appears twice in the dynasty, indicates some connection with Norwegian families, and that the powerful Earl Sigurd Hlodvirsson, the father of Thorfinn the Mighty, had really a son his first-born, named Somerled, while the husband of his great granddaughter, the Sudreyan earl, is called " Gille " (i.e., Gilbrigid, Gilchrist, Gil-Adomnan, Domnansson, or another similar name). It is rather likely that Somerled the elder was a descendant of the Håkons, Canmores, Magnus I, and Dublin and Cearbhall of Ossory. Earl " Gille " by the great granddaughter of Earl Sigurd Hlodvirsson, as well as that of one of Earl Sigurd’s sons Brusee or Thorfinn, was derived from the same common ancestor of Bruce.

The grandfather of Laomainn was the brother of Gilchrist, ancestor of the MacLachlans. This grandfather, Ferchar Lamont, had two sons, Malcolm, father of Laomainn, and Duncan, ancestor of the MacSorleys (Mac Somhairle) of Glassary in West Cowall, the majority of whom later assumed what became the mutual clan-family name of Lamont. The name Lamont appears to date from the middle of the thirteenth century. One feudal charter of that time was granted by Laumanus filius colmi, nepos Duncani, filius Fearchar, conveying lands at Kilmun and Locbgilp to Paisley Abbey, while another, dated 1295, is by colmus filius er haeres domini quondam Laumani. It is from this Lauman that the later chiefs take their name, and are styled Mac-Laomainn. Before the date of these charters the chiefs are said to have been named Mac(F)erachar from their early ancestor, Farquhar, grandfather of Lauman, who lived about the yeare 1200. From a very early time the Lamonts appear to have possessed the greaser part of Cowal, and the ruins of several of their strongholds still remain to attest their greatness. The beginning of their eclipse may be dated from the middle of the fourteenth century.

The Lyons of Glamis in the Strathmore district of Angus descend, according to tradition, from a scion of the Lamonts of Cowall. John the son of Lyon (Johannes fihius Leonis) and Hugo the son of Lyon (Hugo filius Leonis) were members of an inquest on the lands of Rostinot in 1321—1322. John Lyon had a charter of lands in Perthshire ca. 1342—43 from David II. Another John Lyon (or "Lyoun") appears, possibly the son of the former, as clerk and secretary to David II. He was known as the "White Lyon," which suggests an epithetic allusion to the "White Lyon on Blue" of the arms of the Lamonts, his own arms being a reversal of those colors. He was later granted the thanage of Glamis as a free barony by King Robert II ca. 1371—72, and soon afterwards married the king’s daughter. This family later became barons of Glamis (1445) and earls of Strathmore. Some small broken clans in Angus are recorded as petitioning to "be allowed to take the name of Lyon, and be counted clansmen of the Strathmores."

Between Alexander III. of Scotland and Magnus IV. of Norway in consequence of which an entirely new organisation was introduced into the Hebrides, then inhabited by a mixed race composed of the natives and largely of the descendants of successive immigrant colonists of Norwegians and Danes who had settled in the country. Among the leaders sent in charge of the Western garrisons was, according to the supporters of the Irish-origin theory, Colin Fitzgerald, who, under the patronage of Walter Stewart, Earl of Menteith, was settled in the Government of the Castle of Ellandonnan, the well-known stronghold of the Mackenzies of Kintail, situated on a small rocky island at the junction of Lochalsh, Loch Duich and Loch Long.

Among the clans of the West Highlands which appear to be able to claim actual descent from early Celtic stock, Clan Lamont may be considered one of the most assured. There is some reason to believe that the Lamont chiefs were originally a branch of the great house of Ó Neill, kings of Ulster in early times. The hand surmounting the old Lamont crest is pointed to as being undoubtedly the "Red hand of Ulster," and the Lamont motto, Nec parcas nec spernas, is also pointed to as indicating the close relationship, while the documents of early times which refer to the Chief as "The Great Lamont of Cowall " seemed to indicate a relationship with the Ulster title of "The Great O’Neil..,."

In 1334, when Edward Balliol had overrun Scotland, basely acknowledging Edward III.of England as his suzerain, and when, as a consequence of the battles of Dupplin and Halidon Hill, Bruce’s young grandson, Robert the High Steward hid in Bute he escaped to Dunbarton, raised his vassals of Renfrewshire, and stormed the stronghold of Dunoon.  Among those who helped the High Steward on this occasion, was Sir Colin Campbell of Lochow, and when Robert the Steward became King Robert II. in 1371, he made Campbell hereditary keeper of his royal castle of Dunoon. From that day the Campbells used every means to increase their footing in Cowal, and before long a feud broke out between them and Clan Lamont, the ancient possessors of the district, which was to end, nearly three centuries later, in one of the most tragic incidents of Highland history. One of the first episodes of the feud took place in the yeare 1400. The name as Dunoon derives from the name of the castle of Dunhoven or Dunoon which guards the mouth of the Clyde estuary in southern Cowal in Argyll. The name Dunoon (Denune) in the county of Ross is said by Black (`Surnames of Scotland') to be of Campbell origin. At some early date a Duncan Cambel of the Lochawe family and his brother was obliged to flee Argyll and settled with his family in Ross where they took the name Denune. A John Denune died c.1416 as Denune of Davidstoun. A Dunnoven of Pitnelie in Ross was on record in 1574 and an Andrew Denone of Catboll-Abott in 1606 and a John of the same in 1649. However the fact that a `de Denune' appears on record in 1296, whose arms indicate a Stewart-Menteith origin, may offer yet another source for the name. In March 1440 Sir Duncan le Cambel, knight, Lord of Lochawe granted a charter to the parish church of Dun-novyng or Dunoon. From his brother Colin Cambel of Ardkinglas descended the Campbells of Dunoon.

The King’s court was then at Rothesay Castle, and from it, one day, three young lords crossed over to hunt at Ardyne in the Lamont country. As a sequel to their excursion, they tried to carry off some of the young women of Cowal; at which four sons of the Lamont Chief came to the rescue and slew the ravishers.  The King confiscated the Lamont territory in Strath Echaig, and conferred it on the Campbell chief.  Forty years later another incident occurred in which his enemies turned the generosity of the chief of Clan Lamont to account. Celestine, son of Sir Duncan Campbell the Black Knight of Lochow, had died while being educated in the Lowlands during the deep winter snows. Campbell professed to find it impossible to convey the body of his son through the mountain passes to Loch Awe. He accordingly asked permission from the Lamont chief to bury his son in the little Lamont kirk at Kilmun on the Holy Loch. Permission was granted in terms thus translated from the Gaeli "I the Great Lamont of all Cowal do give unto-thee, Black Knight of Lochow, the grave of flags wherein to bury thy son in thy distress." Soon afterwards the Campbell chief endowed the burial-place of his son as a collegiate church, and from that day to this Kilmun has remained the burial-place of the Argylls. In 1472 Colin, Earl of Argyll, obtained a charter of further lands about Dunoon Castle, including the West Bay and Innellan, and the stronghold of Dunoon appears forthwith to have become a chief seate of the Argylls. Still the Lamonts appear to have been willing to act the friendly part to the Campbells.

In 1544, when Henry VIII. was seeking to annex Scotland by forcibly obtaining possession of the infant Queen Mary, and when, to support the enterprise, the Earl of Lennox sailed with an English fleet up the Firth of Clyde, the Lamonts mustered to help the Campbells in defending the stronghold of Dunoon. Lennox landed under cover of the fire from his ships, forced the Lamonts and Campbells to retreat with much slaughter, burnt Dunoon, and plundered its church. A pleasant contrast to that episode was the visit of Queen Mary herself nineteen years later. The Countess of Argyll was the Queen’s favorite half-sister, and it is narrated how Mary, then twenty-one years of age, on July 26th rode from Inveraray and slept at Strone, a Lamont seat; how, next morning, she came to Dunoon, where she spent two days in hunting, and signed several charters; and how on the 19th she rode to Toward Castle, where she dined with the chief of Clan Lamont, Sir John Lamont of Inveryne, before ferrying across to Southannan at Fairlie, on the Ayrshire coast. On that occasion the Queen may have been entertained with music from the famous ancient Celtic harp, which was a treasured possession of the Lamonts for several centuries. In 1640 this harp passed by marriage into possession of the Robertsons of Lude, and it is described and illustrated in Gunn’s elaborate work on the music of the Highlands.

The Lamont territory was in Cowall, where they were the most powerful family until the great massacre of several hundred of their men, women and children by the Campbells in 1646, an act of revenge for the Lamonts’ complicity in the murder of several Campbells by MacDonnells from Antrim a few years earlier. After foolishly surrendering their castles of Toward and Ascog (on the southern extremity of the eastern and western peninsulas of Cowall, respectively) the garrisons, now at the mercy of the Campbells, were cruelly tortured and put to death, and the castles burnt and razed.