Rublev, 23, had previously won tournaments in Doha, Adelaide, Hamburg and St Petersburg and improved to a Tour-leading 39 wins in 2020 -- tied with world number one Novak Djokovic.
"This tournament is really special for me because my grandma was also Austrian, so I have Austrian blood," Rublev said at the trophy presentation ceremony. "It's a really special title for me."
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The in-form Russian won the title without dropping a set at the tournament and needed only two breaks of serve to wrap up the final in 79 minutes.
Victory also sealed his place at the season-ending ATP Finals in London later this month.
Rublev joins Djokovic, Rafael Nadal, Dominic Thiem, defending champion Stefanos Tsitsipas, Daniil Medvedev and Alexander Zverev.
The final spot is still up for grabs and is a toss up between Italy's Matteo Berrettini and Argentina's Diego Schwartzman. Both players will be competing at the Paris Masters that begins on Monday.
Schwartzman withdrew from the Vienna tournament, which allowed lucky loser Sonego to enter the main draw after he lost his final qualifier.
Sonego had a dream run at the tournament, which included the biggest win of his career when he beat Djokovic in the quarter-final.
"This was one of the best tournaments of this year," Sonego said. "It was an amazing final for me. I like Vienna and thank you for all the support."
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Roland-Garros
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