It was the only line built by the original Schweizerischen Südostbahn (Swiss Southeastern Railway).

The line, including a 34.58 kilometre-long section of the Bodensee–Toggenburg railway (Bodensee-Toggenburg-Bahn) that became part of the new Südostbahn as the result of a merger in 2001, has been electrified since 15 May 1939 at 15 kV AC 162/3 Hz.

Finance for electrification was not secured for a long time, but it was eventually approved at the General Meeting on 6 July 1938.

It was scheduled to be completed before the Swiss National Exhibition of 1939 in Zürich (Landi 39).

Electrical operations should have been started on the entire network of the Südostbahn at the timetable change on 15 May 1939.

These were caused by the slope pressures and the cutting of the valley side as a result of the relocation of a cantonal road on the ridge pierced by the tunnel.

Since 2018, all rolling stock up to and including class D4 (22.5 t or 22.1 long tons or 24.8 short tons axle load, 8 t/m (7.2 long ton/yd; 8.1 short ton/yd) linear load) have been allowed on the line.