Dubgall mac Somairle (died 1175) was King of the Isles. He was a son of Somairle mac Gilla Brigte and Ragnhildr Óláfsdóttir. Dubgall was a leading figure of Clann Somairle, and the eponymous ancestor of Clann Dubgaill. Dubgall's career is obscure, and little is certain of his life.

In 1155 or 1156, Dubgall was produced as a candidate to the kingship of the Isles, then-possessed by his maternal uncle, Guðrøðr Óláfsson. Later that year, Somairle defeated Guðrøðr, and the kingdom was divided between them. Two years later, Somairle again defeated Guðrøðr, and assumed control over the entirety of the realm. Whilst is possible that Dubgall was the nominal King of the Isles, it is apparent that his father possessed the real power.

Dubgall's father died in an invasion of Scotland in 1164. At least one of Somairle's sons was slain in this defeat, and it is unknown if Dubgall was present. Whilst it is possible that Dubgall retained a degree of royal authority after Somairle's death, it is evident that his maternal uncle Rǫgnvaldr Óláfsson seized the kingship before being defeated by Guðrøðr. Nevertheless, the territories seized by Somairle in 1156 were retained by Clann Somairle.

Dubgall's next and last attestation occurs in 1175, when he is recorded to have made a donation to St Cuthbert at Durham Cathedral. Whilst Somairle appears to have been a religious traditionalist, his descendants associated themselves with reformed monastic orders from continental Europe. Either Dubgall, his father, or his brother Ragnall, may have been responsible for the foundation of the Diocese of Argyll.

Although the division of Clann Somairle territories is uncertain, it is possible that Dubgall held Lorne on the mainland, and the Mull group of islands in the Hebrides. The date of Dubgall's death is unknown. There is reason to suspect that he was succeeded or superseded by Ragnall at some point. Certainly, Ragnall and yet another brother, Aongus, came into conflict before the end of the century—possibly over the leadership of Clann Somairle. Despite Dubgall's apparent overshadowing by Ragnall, the former's Clann Dubgaill descendants were the most powerful branch of Clann Somairle until the fourteenth century.

Dubgall was a son of Somairle mac Gilla Brigte and Ragnhildr Óláfsdóttir. Somairle's familial origins are obscure, although he was almost certainly of Norse-Gaelic ancestry. Ragnhildr was a daughter of Óláfr Guðrøðarson, King of the Isles. The union of Somairle and Ragnhildr may date to about 1140. According to the thirteenth- to fourteenth-century Chronicle of Mann, the couple had several sons: Dubgall, Ragnall, Aongus, and Amlaíb. There is reason to suspect that Dubgall was the eldest of these sons. Certainly, near contemporary sources such as the chronicle and the thirteenth-century Orkneyinga saga list his name before those of his brothers. Dubgall's name is Gaelic. The mixture of Gaelic and Scandinavian names borne by Somairle and his sons appears to exemplify the hybrid Norse-Gaelic milieu of the Isles. The marriage between Somairle and Ragnhildr had severe repercussions on the later history of the Isles, as it gave Somairle's descendants—Clann Somairle—a claim to the kingship by way of Ragnhildr's royal descent.

The year 1153 marked a watershed in the history for the Kingdom of the Isles. In June of this year—whilst Óláfr's son, Guðrøðr, was absent in Norway—Óláfr was assassinated by three Dublin-based nephews. Within months, Guðrøðr was able to overcome his kin-slaying cousins, and thereby secured kingship for himself. During the latter's reign as king, both Guðrøðr and Somairle appear to have involved themselves in military campaigns in Ireland. In 1154, for instance, troops from the Isles and the western seaboard of Scotland certainly supported Muirchertach Mac Lochlainn, King of Cenél nEógain in a defeat against the latter's rival Toirrdelbach Ua Conchobair, King of Connacht. Guðrøðr further appears to have unsuccessfully attempted to secure the kingship of Dublin. However, these setbacks suffered under Guðrøðr's rule—perhaps coupled with the rise of Muirchertach's influence in the Isles—may well have incited Dubgall's father to seize the initiative.

In 1155 or 1156, the Chronicle of Mann reveals that Somairle conducted a coup against Guðrøðr, specifying that Þorfinnr Óttarsson—described as one of the leading men of the Isles—produced Dubgall as a replacement to Guðrøðr's rule. The fact that the chronicle identifies Dubgall as the chosen son seems to be further evidence that he was the senior-most of Somairle's sons. Nevertheless, Somairle's stratagem does not appear to have received unanimous support, as the chronicle specifies that the leading Islesmen were made to render pledges and surrender hostages unto him, and that one such chieftain alerted Guðrøðr of Somairle's treachery. Late in 1156, on the night of 5/6 January, Somairle and Guðrøðr finally clashed in a bloody but inconclusive sea-battle. According to the chronicle, Somairle's fleet numbered eighty ships, and when the fighting concluded, the feuding brothers-in-law divided the Kingdom of the Isles between themselves.