29-year-old Pole claims biggest win of his career with victory in Austria.
The 29-year-old entered the competition with a 9.1-point lead over Norway's Marius Lindvik, the upstart contender who won in Garmisch-Partenkirchen and Innsbruck for his first two career World Cup triumphs. Germany's Karl Geiger and Japanese defending champion Ryoyu Kobayashi were both also within 14 points before competition.
However, Kubacki, the hill record holder at Bischofshofen with a 145.0-metre jump, outperformed all his rivals to win just his second career individual World Cup, and take home one of ski jumping's most prestigious trophies in the process.
He celebrated his 140.5-metre second jump by collapsing into the snow at the bottom in delight.
Kubacki qualified for the first round of the final in only 13th, behind Kobayashi and Lindvik but ahead of Geiger.
That meant that in the first round, the German would be the first to jump, and he leapt an impressive 140.0 metres to take the lead on 147.7 points after 20 athletes.
But Kubacki was in no mood to be upstaged, jumping 143.0 metres – just two metres shy of his hill record – and scoring 151.6 points to extend his Four Hills overall lead over Geiger from 13.3 points to 17.2 points.
Lindvik and Kobayashi were both unable to clear the 140-metre mark in their first jumps, dropping them further behind the Olympic team bronze medallist Kubacki and ending Kobayashi's hopes of retaining his Four Hills title, although Lindvik remained second overall in the tournament standings.
With Kubacki, Geiger, and Lindvik leading after the first round, the three Vierschanzentournee contenders would be the last to jump in the second round.
Lindvik, the young Norwegian, was the first of the final three to jump.
He managed 137.0 metres for a total of 289.4 points, guaranteeing a spot on the podium in both the event and the Four Hills.
Geiger's subsequent 136.0-metre jump for a 291.0 total was enough to overtake Lindvik in the hill event and put him into first, although it wasn't enough to put him past the first-timer in the overall tournament standings.
But no one could take the glory away from Kubacki, who jumped 140.5 metres and cracked the 300-point total margin with a 300.9 total.
Kubacki's final Four Hills total was 1131.6 points, 20.6 points ahead of Lindvik. Geiger was third and Kobayashi fourth.
"It was quite an emotional day," he admitted to Eurosport afterwards.
"It feels unbelievable for me, I made a really strong jump today and I was really satisfied with the work I've done on the hill.
"There were many strong jumps and I'm satisfied I managed a high level and win this last tournament. I couldn't manage a win before. I'm really happy."
He becomes the first Polish winner of the tournament since Kamil Stoch achieved the feat two seasons in a row in 2016/17 and 2017/18.