Donald, 8th Earl of Mar was born around 1302 in Saline, Fife, Scotland. His father was Gratney (or Gartnait), 7th Earl of Mar, and his mother was Christian Bruce, sister of Robert I of Scotland. In 1332 Donald became regent of Scotland for the young King David II, son of Robert I.

Following the invasion of Edward Balliol, with the support of Edward III, Mar led the Scots loyalists to defeat at the Battle of Dupplin Moor on August 12, 1332 and died in battle.

Through his marriage to Isabella Stewart they had a son Thomas, and a single daughter, Margaret de Mar who succeeded her brother and became Countess of Mar.

See also: the Earls of Mar