The win was Siniakova's eighth women's Grand Slam doubles crown and Gauff's first.
Their makeshift pairing only came together days before the start of the French Open, after the American's regular partner Jessica Pegula withdrew from the tournament.
"Thank you, Katerina, for playing with me, we decided to do it two days before the tournament started," said Gauff, a doubles finalist at the 2022 French Open.
"It was very last minute, I wasn't planning on playing doubles, so thank you for asking me."
![Action during the match Action during the match](https://livesport-ott-images.ssl.cdn.cra.cz/r900xfq60/39c507a9-12d3-4b99-b095-06715583e499.jpg)
The first hour of the match was largely dictated by Errani and Siniakova's struggles on serve, as both were broken twice each, with the first set going into a tiebreaker.
A quick start there gave Paolini and Errani a 5-3 lead, but Siniakova raised her game to win some key points that turned the tide in her and Gauff's favour.
The Italians began the second set with real intensity, earning four break points in the first game, but Gauff and Siniakova battled back for a crucial hold before going up a break to take a 2-0 lead.
That appeared to take the wind out of Errani and Paolini's sails, and though they were able to twice bring the second set back on serve, Gauff and Siniakova broke for a third time in the second to take a 5-3 lead.
Gauff, who has often misfired with her revamped serve in recent months, showed no nerves when it mattered most and comfortably held on to clinch the win.
Paolini, who suffered a 6-2, 6-1 defeat to Iga Swiatek on Saturday, was left looking dejected.
"It's been two very intense weeks for me, very nice but very emotional," the Italian said.
"I have a lot of memories and I can't wait to be back here."
Gauff's win also earned her a measure of revenge on Paolini and Errani, who defeated the American and her Australian partner Erin Routliffe in the final of the Italian Open in Rome last month.
Despite the defeat, five-times Grand Slam doubles champion Errani said her and Paolini's ambitions of winning the Paris Olympics were still strong, adding: "We'll be here in one month. We have a dream, and it'll be special to play the Olympics in this place."