The battle itself took place where Donald chose to camp, near Harlaw, two miles north of Inverurie. Harlaw has been described as a town, but it was more likely to be a 'fermtoun'. Typically these comprised several families and a number of houses.
Donald's forces chose a strong defensive position in this predominantly farming country they stopped on a plateau, which was surrounded by wet land to the east and west. Mar broke camp and crossed the River Urie. Mar split his men into two divisions and the vanguard was led by the sheriff of Angus and constable of Dundee leading the Angus and Mearns men.
Donald's forces were rallied by a battle song, which also shows that Donald's forces were in three divisions. Red Hector of the Battles, Hector Roy Maclean of Duart, was Donald's overall general, leading the forces on the right wing, at the head of his clan. The left wing was led by Callum Beg, chief of the MacIntoshes, whilst Donald commanded the central battle force. Mar's vanguard was lead by Scrymgeour and Sir Alexander Ogilvy, sheriff of Angus. The vanguards clashed probably near to where the present day monument stands.
The battle was probably entirely fought on foot. The wealthier lairds and knights may have worn plate armour. Chiefs on the Donald side may well have worn mail with a conical helmet and jupon, a jacket or tunic worn over or under armour. The main body of the men, on both sides, would have been armed with lances, spears, axes and swords and would not have worn armour, or anything that would have weighed them down.