He will be facing Australia's Alex de Minaur, who defeated Spain's Jaume Munar 3-4 (5/7), 4-1, 4-1, 3-4 (4/7), 4-2.
Both have made remarkable strides this season.
In the absence of Alexander Zverev, who skipped the event for the second year after qualifying for the ATP Finals, Tsitsipas was the top seed.
De Minaur is now an impressive 28-22 on the year after entering 2018 with just two tour-level match wins to his record.
Just like de Minaur, Tsitsipas, the top seed and the best-ranked player in the draw, will also be arriving in the finals undefeated.
The top seed claimed the title by winning all five of his matches during the week, to succeed South Korea's Chung Hyeon, who won the inaugural edition a year ago in which Tsitsipas only played an exhibition match.
Tsitsipas - whose looks have been compared to legendary Swede Bjorn Borg - has an aesthetically pleasing one-handed backhand and more natural power than his opponent, while possessing plenty of fight of his own.
It remained hard to split the pair in the third, with a tiebreaker required at 3-3, but it was the Greek who stepped up to get himself in front for the first time in the match.
He said he didn't know how he recovered from those match points.
'I have huge respect for him, his game and his personality. It was a fantastic match, I stayed calm. "I was mentally very strong and that was proven in the tie-break in the last set". It's a shame it couldn't finish with a win but I couldn't be prouder.
De Minaur was at his gritty best against Fritz earlier in the week to save five set points in a tiebreak and claim the opening set before running away with a 4-3 (10-8) 4-1 4-2 victory in his final group stage match in Paris.
"Overall I'm very happy with my performance", said the player from Sydney.
He said winning the final would be "the cherry on top of an unbelievable season for me".