The Thörlerbahn opened on 17 November 1893 as far s Thörl, and four days later to Au-Seewiesen, but was never extended to meet the Mariazellerbahn (using the same gauge, and opened in 1907), for financial reasons.

22.9 km long, the line originally had eleven stops, at Kapfenberg (Südbahn and Lokalbahn); Hsts. Winkel, Hansenhütte and Margarethenhütte; Bhfs. Thörl and Aflenz; Hsts. Wappensteinhammer and Hinterberg; Bhf. Seebach-Turnau, and the terminal Bhf. at Au-Seewiesen. Hst. Einöd was opened later. The original station at Kapfenberg was made into a junction, with transfer facilities, but the passenger accommodation was not altered.

The single track railway passed coal deposits, iron manufacturers, and dense wooded areas on its way up the winding valley of the Thölgraben. Two short branches, at Bhf. Thörl and Hst. Margarethenhütte served factories beside the line.

The lack of space available at Kapfenberg Südbahn meant that the station did not have sufficient room for narrow-gauge tracks as well as standard gauge ones, and 600 metres of 4-rail, later changed to 3-rail, track were laid to reach Lokalbahnhof, later called Kapfenberg Landesbahn. The 4-rail section allowed the transfer of standard-gauge rolling stock using narrow-gauge locos.

For the opening in 1893 C-type locos developed by Krauss in Linz were provided , similar to the C1 type of Austrian narrow-gauge locos. In 1898 four more engines of the same type, designated Series Z, were supplied to Pinzgauer Lokalbahn. The Thörlerbahn purchased Clt-nP "Graz", again made by Krauss, in 1896.

The rolling stock comprised 4 1st/3rd class coaches, 4 3rd class coaches, 2 combined post and equipment vans, 6 closed and 24 open wagons, a snow plough, 1 Draisine inspection trolley and 3 trailers as well as an "insert" wagon, which ran on narrow-gauge tracks and was designed as a convertor wagon for standard-gauge and narrow-gauge stock. Latterly one of the locos was fitted with an extra coupler, and the wagon laid out of use. Unable to make a profit, the Federal Railway sold the concession to Steiermarkische Landesbahnen (StLB) from 1 July 1922.

While there was abundant goods traffic from and to Thörl – indeed the line ran close to apacity - the line lacked the potential for passenger traffic. While the route provided access to the scenic and mountainous area of the Hochschwab, it was a long way from any major settlements, and scheduled passenger service was discontinued as early as March 15, 1959.

The first diesel loco, a D40 acquired from SKGLB (Salzkammergut Lokalbahn), arrived in 1958, to be followed in 1964 by a main-line loco, and in 1971 by the heavy-duty VL21 diesel loco bought from DB (Deutsche Bahn). Two additional diesel locos were purchased by Steiermärkische Landesbahnen (StLB) from the Yugoslav narrow-gauge lines of Bosnia.

Goods traffic wilted in the face of road competition, and ended beyond Seebach Turnau from 31 December 1990, and the track was dismantled. A private association, the "Thoerlerbahn" organized steam excursions starting in 1991 between Kapfenberg and Seebach Turnau. Goods traffic ceased on the rest of the line from 31 December 1995, leaving only transfer traffic within Kapfenberg. A majority of the StLB vehicles were transferred to the Murtalbahn and Feistritztalbahn. The steam excursions ceased in 1999 and the "Thoerlerbahn" went into bankruptcy. Their vehicles were taken over by Club 760 and Club U44. The line was removed in 2004. S tation buildings remain along the route.

At least one of the coaches used on the line has survived. It was built by Grazer Waggonfabrik in 1892, as StLB Ci202 for the line at Stainz. In 1932 StLB transferred the coach to the Thörlerbahn, as C51. In 1969 it moved again, to Murau. It was donated to Club 760 in 1974, and the upperworks were stripped down and repaired by the StLB at their Murau workshops. The Zillertalbahn made further repairs in 2000.

One of the locomotives used on the Thörlerbahn is still in seasonal use, having been purchased by Club 760 in 1972 - their first steam engine. The loco was one of the original engines on the Thörlerbahn, and was named "Thörl". Apart from a spell on the Stainzerbahn for five years up to 1950, the locomotive seems to have stayed on the Thörlerbahn until set aside by StLB in 1970. The locomotive was put back into running order in 1994, and was leased to the private railway at Kapfenberg, from where it returned when the museum line ceased trading. The locomotive is now on the Taurachbahn.