The Heritage Paths website only maps Comyn's Road between Glen Tromie and Blair Atholl, as the part from Ruthven Barracks to Glen Tromie is included here as part of The Minigaig. However, if travelling along Comyn's Road from end to end, it perhaps makes more sense to start from Kingussie or Tromie Bridge, so that's the route description we've provided below.

From Kingussie, walk to the ruins of Ruthven Barracks where a farm track heads south for about 1mile/2km until a slightly overgrown track goes to the right. This improves after a short distance when a more used track comes from the left and runs through to around the west side of a knoll at NN758956. From this point the route heads through the col to the east of Sron na Gaoithe, then heads south by Carn Pheigith to the Dailriach bridge* over the Tromie. At this point the historic route stays on the west side of the Tromie until the Allt na Fearna just beyond Bhran Cottage. However, this side of the river has no obvious path and it is easier* to cross Dailriach bridge* and follow the tarred road until Bhran Cottage. This point can be reached more easily by starting from Tromie Bridge and walking up Glen Tromie on the tarred road. At Bhran Cottage a modern gravel track leaves the tarred road and fords the Tromie before crossing the Allt na Fearna and heading onto Druim an t-Seilich. The ford is large and potentially dangerous at about 20m wide and 50cm deep, but about 100m upstream from the ford there is a footbridge* (hidden in trees) over the Tromie which also avoids the smaller ford over the Allt na Fearna on the modern track (the surveyor wishes he had found the bridge* first!). This track continues to climb Druim an t-Seilich as a gravel track deteriorating into a peatier track onto Maol an t-Seilich. At this point the track ends but there is a continuation as an ATV track rising slightly and then becoming a narrow footpath. The surveyor followed this and it becomes a descending traverse of the steep slopes of Bogha-cloiche on what were more like deer paths towards Gaick Lodge. Previous published accounts state that there is a pony track from Maol an t-Seilich to Gaick Lodge and on descending to the lochside just before Gaick, part of this track appeared to be found, but the surveyor could see no obvious pony track on Maol an t-Seilich, nor was the section found at the lochside in particularly good condition. It is assumed that the track has been little used for many years.
Once on the grassy flats at the southwest end of Loch an t-Seilich a track is found which leads to the Abhainn Ghaig opposite Gaick Lodge. There has been a bridge here but it is washed away and a potentially dangerous ford must be made of the river to reach the lodge. Once across the river a good track leads by the lodge and south to the Allt Gharbh Ghaig (part of the Gaick Pass route). Just before this river is forded a track heads left up the Allt Gharbh Ghaig. This track crosses the first burn (with footbridge), and then crosses two outflows of the Allt Domhainn neither of which had visible water on the visit but appeared likely to be potentially difficult in wet weather. Shortly after this the track runs into flood debris and 2 options are possible. The first is to attempt to follow the track which can be found crossing the burn a couple of times on grassy flats before ending on the west side of the burn at a bridge. This was easy to do on the visit as the burn was low and stepping stones plentiful, but in wet weather it could be difficult. The alternative is to follow a footpath through heather on the east side of the burn to the bridge at about NN774819 and cross to the west side.
A small track (the old road?) then crosses the outflow of the Allt a Chapirnich which had very little water but a deep rough stony bed, and again might be difficult in wet weather. From this point Comyn's Road is picked up climbing a zig zag and traversing the steep slopes above the burn onto the plateau of Bac na Greige. On this plateau it is thought that Walter Comyn met his terrible end falling from his horse which galloped away severing a leg and leaving his body by the road. The old road can be followed with some care and has a number of cairns on it until on Bac na Greige a small upright stone appears to mark the crossing point on the plateau. From here the road is less obvious for a stretch until it is picked up more clearly on the descent to Feith na Mad where it fords the burn and climbs the slope towards Sron a' Chleirich. The road is not really obvious on this stretch but skirts a small top at Carn an Fhiadhain before descending to another ford on Allt a' Mhuillin on the W side of Sron a' Chleirich. The road can be found dropping to the ford and rising across the slopes of Sron a' Chleirich. The ford is at the top of a steep gully which has eroded over time and a slight detour upstream makes the crossing easier and safer.
From here the road can be followed west of the summit and starts to descend the south shoulder before disappearing. The surveyor took a direct line from here to the old sheilings on the Allt a Choire Bhig down a steep initial slope and then across pathless heather moor until a burn is met running in a deep trench at which point it was easier to drop to the Allt a Choire Mhoir which can be followed down to the sheilings with a couple of crossings of the burn which was fairly easy with little water but may again be difficult in higher water judging by the burn bed. (It may be worth noting that there is a track met on the summit of Sron a' Chleirich, and there is a track from the sheilings heading towards Sron a' Chleirich. They may be the same track which would provide an easier descent (or ascent) but as the track appears to head down the shoulder of the hill from the top to the southwest but not towards the sheilings the surveyor did not have sufficient faith in it to follow it. It may just loop to avoid the steeper descent.)
At the sheilings a grassy track is followed northeast, fords the Allt a Choire Bhig and heads uphill and southeast as a gravel track to Clunes bothy. From the bothy the route heads southeast (ignoring an old track which appears to head too far east) and once the brow of the slope is reached heads directly towards Ruichlachrie which can be seen in the distance (weather permitting). There is no path across this part of the route. On descending to Cuilltemhuc the route crosses the main Glen Bruar track and heads to the Bruar Water which is forded and the track continues by Ruichlachrie as a good track until it meets another estate track at the forest edge. Turning left it heads southeast by Glen Banvie to Blair Castle and the village. Note that the Bruar ford is very shallow and in Highland Highways Old Roads in Atholl, Kerr states that it is due to diversion for hydro electricity purposes, but if the river was too high to cross the Bruar track could be followed to Calvine.

*Newsflash: both the Dailriach bridge and that near Bhran Cottage were reported in May 2018 as having been washed away; the river crossings may thus be very difficult, so it may be easier to stay on the west side of the Tromie after all. Many thanks to John Davidson's excellent article A Minigaig Adventure which gives an idea of what to expect on the first section of Comyn's Road from Ruthven to the River Tromie.

OS Landranger 43 (Braemar & Blair Atholl) & 42 (Glen Garry & Loch Rannoch area)