The Mariazellerbahn begins at the St. Pölten Hauptbahnhof railway station. Right after leaving the station, the line passes through a tunnel under the "Leobersdorfer Bahn", another railway serving St. Pölten. The "Alpenbahnhof" that comes right after that was, until the construction of the new Laubenbachmühle operating centre, the railway's main operational center. The rolling stock sheds, workshops, and extensive freight facilities are now largely used for storing surplus rolling stock. Next, the railway quickly leaves the town and passes through hilly, farmed land for the first few kilometers, south of St. Pölten from the Traisen valley into the Pielach valley. The route quickly reaches the biggest station on the line at Ober-Grafendorf, which includes the junction with the abandoned branch line.