In 1324 Agnes married Patrick, ninth earl of Dunbar and March, governor of Berwick. She was his second wife. When Berwick became occupied by English forces in 1333, Patrick decided to join the English, and Edward III granted Agnes and Patrick English lands. Patrick was given permission from Edward to refortify Dunbar Castle. Patrick switched back to the Scottish side. Agnes was deeply angry with her husband from him switching loyalties, but Patrick was also suspicious of her. It seems that there were no surviving children of the marriage between Agnes and the Earl. She died just a few months before him.