Although the details of Alexander's early life are largely unknown, he appears to have succeeded to his father's position as Lord of Argyll and Lorne and head of the MacDougall kindred after the latter's death in 1268.
Under the latter's authority, Alexander was involved in the Scottish expedition that quelled a revolt on the Isle of Man in 1275.
He was married to the sister of John II Comyn, Lord of Badenoch, key ally and kinsman of the Balliols.
Alexander was captured during the Battle of Dunbar by English forces and was imprisoned at Berwick Castle until his release in 1297.
The murder of Alexander's kinsman John III Comyn, Lord of Badenoch in 1306 by Robert de Brus, Earl of Carrick, hardened MacDougall's anti-Bruce position, and this became opposition to Robert's kingship as the latter was crowned King of Scots at Scone later in the year.