Gartnait, Earl of Mar was born in Scotland to Domhnall I, Earl of Mar (-bef1303) and Helen and died 1305 Scotland of unspecified causes. He married Christina Bruce (c1278-c1356) in Scotland.
Gartnait of Mar - Gartnait mac Domhnaill (Gartnait, Donald's son) - was the eighth known Mormaer of Mar, ruling from somewhere around 1301, perhaps as early as 1297, until his death in 1305. He was a son of Domhnall I of Mar, brother of Isabella of Mar and brother-in-law of Robert I of Scotland.
We last hear of his father alive in 1297, and we hear of his son Gartnait as Mormaer perhaps in 1302, and definitely by 1305. Gartnait himself is known to have collaborated with Edward in some form during the crackdown of 1297, but this does not necessarily mean any break with his father or with Robert I, whom his father supported.
In 1302, a document containing terms of reconciliation between Edward I of England and Robert stipulates that Robert should act as warden of Gartnait,1 implying that Gartnait's father Domhnall had just died.
Children
| Name | Birth | Death | Joined with |
| Domhnall II, Earl of Mar (c1302-1332) | 1302 Saline, Fife, Scoland | 11 August 1332 Battle of Dupplin Moor, Scone, Perthshire, Scotland | Isabella Stewart (-c1332) |
Siblings
| Name | Birth | Death | Joined with |
| Gartnait, Earl of Mar (-1305) | Scotland | 1305 Scotland | Christina Bruce (c1278-c1356) |
| Isabella of Mar (c1277-1296) | |||