Coming from Graz:
A9 Phyrnautobahn north, then S35 Brucker Schnellstraße and S6 Semmering Schnellstraße to Kapfenberg exit, then on the B20 (Mariazeller Bundesstraße) 49 km north (signpost).
Variant: S6 Semmeringschnellstraße to exit St. Marein and then over the Pogusch to Turnau and from Au on the B20 to Mariazell.
Coming from Salzburg:
Westautobahn A1 to exit Ybbs, then B25 to Scheibbs, from there two options: Either B28 via Wastl am Wald to B20, then via Annaberg and Josefsbergor B25 further to Grubberg and then B71 via the newly expanded Zellerrain.
Coming from Vienna: Take the A1 Westautobahn to the St. Pölten Süd exit, then the B20 (Mariazeller Bundesstraße) 76 km south, either via Annaberg and Josefsberg or in Freiland turn left from the B20 onto the B21 and continue via Hohenberg and St. Aegyd through the Halltal valley to Mariazell (sufficiently signposted).
Alternative: Südautobahn A2 and S6 Semmering Schnellstraße to Mürzzuschlag, then via Neuberg and Mürzsteg on the B21 to Mariazell.
Detailed information on how to get there can be found here: