It is 118 mi (190 km) long and runs through the central Scottish Highlands, mainly following the route of the A9, and linking a series of small towns and villages with Perth at one end and Inverness at the other.

[5] Other distinct features on the route include the viaducts at Culloden and Tomatin, the spectacular mountain pass at Drumochter and the severe gradients encountered in both directions, particularly the extended climb from Inverness to the Slochd summit which averages around 1 in 60 the whole way.

[7][8] In March 2019 Network Rail completed a programme of works to increase capacity on the line and support the introduction of InterCity 125 sets on ScotRail services, with passing loops and platforms extended.

The Caledonian Sleeper travels overnight between Inverness and London Euston via the West Coast Main Line.

South of Edinburgh it forms the longest locomotive-hauled passenger train in the United Kingdom, with 16 coaches.

On Sundays, a couple of services continue through to Elgin, calling at Nairn and Forres.