In administrative terms, in the reign of James vi, the Borders were divided into three sections. These included the area stretching back some miles from the frontier line itself, which formed the administrative regions of the East, Middle and West Marches. There was a similar framework to the south of the border which formed the English East, Middle and West Marches, though their boundaries did not meet their Scottish counterparts at the same points on the frontier. The national frontier of the the Scottish Middle March coincided with half of that of the English East March and all of the English Middle March, with its last eight miles adjoining the English West March. Thus the Scottish Middle March's stretch of frontier was the longest and involved its officials in interaction with their counterparts in all three English Marches.

The physical geography of the region and its medieval administrative areas, the sheriffdoms, determined the internal divisions between each Scottish march. The Middle March comprised the shires of Roxburgh, Peebles and Selkirk and included the lordship of Liddesdale, which fronted onto the border. The Moorfoot Hills marked its northern edge, whilst the hills of the Southern Uplands formed a barrier to the West March. The outer edge of the Merse, to the east, sloped down into the East March. The topographical layout of the land, particularly the moor-covered uplands of the western half of the march, lent itself to an image of remote wasteland. However, it was not inaccessible, the rivers cutting through it providing corridors of communication: the valleys of upper Tweeddale and Teviotdale and the rivers Jed, Ettrick and Yarrow facilitated communications within the region, whilst those of the Leader and Gala rivers gave access northwards to Edinburgh through the passes of Soutra and Fala respectively. Its principal towns were Jedburgh, Selkirk and Peebles, the administrative centres of its sheriffdoms, and Kelso, Melrose and Hawick.

The day-to-day administration in the marches, as elsewhere in Scotland, was led by its resident sheriffs; in the Middle March these were the sheriffs of the shires of Roxburgh, Selkirk and Peebles. The march, however, had an extra layer of officialdom, which was peculiar to the Borders, the warden whose primary duty was concerned with the regulation of cross-border affairs.