Càrn Mairg is usually climbed from Invervar (grid reference ) in Glen Lyon as part of the circuit of the four Carn Mairg group Munros. For many years parking was a problem on the narrow road but the car park built by the Chesthill estate has eased this difficulty. The clockwise circuit follows the Invervar Burn for just over a km until the forest is left behind, then the first Munro of Càrn Gorm can be climbed by going west, the route then goes to Meall Garbh before reaching Càrn Mairg. Navigation throughout the walk is aided by a dilapidated line of old rusting fence posts which follow the ridge. A direct ascent is possible from Fortingall (grid reference ) up Gleann Muilinn but this is a round trip of around 20 km. The summit is marked by a large cairn of quartzite boulders and gives a fine view of Schiehallion to the NE (see picture).