The railway company was established as a result of British Aluminium's plan to build an aluminum plant in Orsières.

The branch line from Sembrancher to Le Châble was opened on 5 August 1953 and served the construction of the Mauvoisin power station.

The destroyed Bt 31 control car was replaced by a similar vehicle from the Régional du Val-de-Travers (RVT).

[4] The MO merged with the Martigny-Châtelard Railway to form the Transports de Martigny et Régions (TMR) on 1 January 2000.

The MO procured three ABDe 4/4 EAV (Eidgenössischen Amt für Verkehr—"Federal Office of Transport") railcars (6–8), three associated Bt control cars (31–33) and two standard passenger coaches (Einheitspersonenwagen).

In 1983, a fourth, identical railcar was acquired from the Régional du Val-de-Travers (RVT) and classified in the rolling stock fleet as ABDe 4/4 9.

[7] From there, TMR bus services continue to Champex, Val Ferret or the Great St Bernard Pass.