This happened a few times in Austria, though not recently on the national level.
Here is a diagram of National Council election results since Austria became a republic. If that diagram is correct: In 1920 and again from 1971 the National Council had 183 seats, of which a majority is 92 seats, which the SPÖ (red, Sozialdemokratische Partei) achieved in the 1970s under Bruno Kreisky. Between that, the National Council had 165 seats, of which a majority is 83 seats, achieved by the Christlichsoziale Partei (pre-WW2) and its successor, the ÖVP (after WW2) (both black) a few times too.
Those two large parties have, as can be seen on that diagram, become a lot less relevant in more recent decades.
How was it achieved? The best sources I have available are textbooks that were used in Austrian schools which explain the following as factors for Bruno Kreisky's success.
According to "Zeitbilder 4" (1st edition reprinted in 2006, ISBN 3-209-03767-1):
- The SPÖ was able to win over some bourgeois and liberal voters and changed from being a "pure workers' party" to a "left-wing people's party".
- Kreisky buried the traditional animosity between church and party and declared that every religious person could also be a socialist.
According to "Zeitbilder 7&8" (1st edition from 2006, ISBN 978-3-209-05449-4):
- Kreisky stopped using the (in his mind outdated) term "working class".
- He won over young male voters by shortening mandatory military service.
On the subnational level in Austria, this is more common, including more recently. I can't find such a nice diagram as above, but this table has the results for the Second Republic and this table for the First Republic. You can see for example that absolute majorities for the SPÖ have historically been common in Vienna (where other parties basically just campaign on wanting to be the SPÖ's coalition partner) and for the ÖVP in many other states like Tyrol, Vorarlberg and Lower Austria. This is mainly because the SPÖ is the traditional representation of the working class (large proportion of the population in Vienna) and the ÖVP that of those who work in farming or tourism (many people in rural areas).