Mairead nighean Eachann (English: Margaret, daughter of Eachann; 1356–1408) was the consort of Alexander Stewart, Earl of Buchan (also known as the "Wolf of Badenoch") and mother of Alexander Stewart, Earl of Mar.
She is mentioned in the Moray Registrum, which gives her name in Latin and informs us that she came from the lands within the sphere of the bishopric of Ross. She has been described as the Wolf's wife "by Gaelic secular marriage", referring to the fact that the marriage was irregular in church custom and that the Wolf was already married to Euphemia I, Countess of Ross. In 1389, Countess Euphemia, complained to Pope Clement V that her marriage to Buchan was meaningless as the Wolf was cohabiting with Mairead, and the pope subsequently annulled the marriage in late 1392.
The Wolf continued his cohabitation with Mairead through the 1390s. The Wolf had seven "bastard" children, all perhaps the children of Mairead. These were Alexander, Sir Andrew of Sandhauch, Donnchadh, James, Walter, Robert, and Margaret (who married the 6th Earl of Sutherland).