The railway is operated by NÖVOG, which is owned by the provincial government, and is a part of the Verkehrsverbund Niederösterreich-Burgenland (Lower Austria and Burgenland Transport Association).

The gauge of 760 mm (2 ft 5+15⁄16 in), as with all narrow-gauge railway undertakings in the Danube Monarchy, was made necessary by the military administration.

Rolling stock used in military service on railways in Bosnia and Hercegovina was 760 mm gauge and would need to be brought in.

For the opening of these lines, the Lower Austrian State Railways bought four U Series steam locomotives, already proven on the Murtalbahn.

The locomotives along with the two-axle passenger coaches and goods wagons, which were customary at the time, formed the railway network's basic equipment.

Among the various kinds of freight carried on the railway were agricultural products, ores from local mines, and wood from the heavily forested mountain region.

Wood remained the most important kind of goods on the Mariazell Railway right up until freight operations were discontinued.

Several scenarios for raising the railway's performance were considered, among them double-tracking and the acquisition of an even stronger type of steam locomotive.

[citation needed] The only electric traction at this time was to be found on tramways and light, local railways, which used only direct current (DC) throughout.

They were also used to supply the region with electricity, thereby laying the groundwork for the Lower Austrian state energy company NEWAG, now known as EVN.

That, and the rebuilding of the rolling stock in the 1950s and 1960s, as well as the changeover to diesel working on the branch line were the furthest-reaching modernization measures undertaken on the railway.

Between 1959 and 1962, the original electric locomotives, now known as ÖBB class 1099, were given new, more modern style, bodies, whilst retaining the same traction equipment.

Freight service still continued for a few years as far as Schwarzenbach an der Pielach after it had been discontinued to Mariazell, but it was limited to wood carried in narrow-gauge wagons.

In the autumn of 2003, a plan was drawn up to convert the line between St. Pölten and Kirchberg an der Pielach to standard gauge, as this stretch was considered important for commuters and school children.

As part of this transfer, NÖVOG announced plans to modernise the line at a total cost of €117m, including €65m on new rolling stock, €20m on a new depot, €20m on infrastructure, €7.5m on the overhead electrical supply and €4.5m on signalling.

In order accommodate the new trains and provide a new operating centre for NÖVOG, a new station with depot and workshop was built at Laubenbachmühle between 2011 and 2013.

The final unit was delivered in January 2014, allowing the full normal service of the line to be operated with such trains.

The large new station and depot at Laubenbachmühle, designed to blend into the surrounding landscape, is now the line's main operating centre.

This stretch of the line is said to be the railway's greatest highlight for those with great romanticism for the wild: In between, along a row of short tunnels, the traveller gets a look into the Zinken ("tines"), as the craggy Erlauf gorge is called here.

Whilst this station serves the pilgrimage center of Mariazell, it is actually located some 1 kilometre (0.62 mi) north in the municipality of Sankt Sebastian.

Connection is made here with the Museumstramway Mariazell-Erlaufsee, a standard gauge heritage steam tramway that operates to the nearby Erlaufsee.

Museumstramway Mariazell-Erlaufsee is planning to take over a short part of the right-of-way for a project to build a tram line from the railway station into town.

The now largely closed branch line was known to locals as the Krumpe (Lower Austrian dialect form of the word krumm, meaning "crooked" in German), as a reflection of its indirect nature.

It left the main line at Ober-Grafendorf and was an unelectrified branch that lead through the foothills of the Alps in a roughly westerly direction by way of Kilb, Mank, Sankt Leonhard am Forst, Ruprechtshofen and Wieselburg an der Erlauf to Gresten.

The three-car articulated EMUs are designed to operate up to 80 km/h, and are prominently branded Himmelstreppe ("Stairway to Heaven"), a name chosen to reflect the line's terminus in the pilgrimage centre of Mariazell.

This was a private initiative in the 1990s by several Mariazell Railway employees who managed to fetch back the Mountain Line's original locomotive.

Due to its history and early provenance, the Mariazell Railway is run on the unusual voltage of 6.5 kV and frequency of 25 Hz, provided by its own supply from the EVN power company.

Even today – although the public supply has been changed to three-phase at 50 Hz – about 21 km of community power lines are still in service.

An old, smaller inverter set in Erlaufboden and two old 25 Hz machines in Wienerbruck power station serve as reserves for the railway.

The substations at Gösing and Rabenstein are run and overseen remotely by the EVN system operator in the company headquarters at Maria Enzersdorf.