The 28-year-old won through 3-6, 6-0, 7-5 in a clay-court battle which lasted two hours 23 minutes in the Swiss resort.
Cachin had not dropped a set in his run to the final, ousting top seed Roberto Bautista Agut in the second round.
On Sunday, Ramos-Vinolas struggled after the first set, calling for courtside treatment for blisters.
The 2019 Gstaad winner failed to win a game in the second set, but despite rallying in the third set missed a chance to lift a fifth career title at the age of 35 years.
"In the beginning of the match I was a little nervous and made a few mistakes," said Cachin who climbs to a career-high 49 in the world rankings.
"It was the first time I had played against a lefty in the tournament but I stayed there.
"I tried to be positive, more aggressive and go to the net. In a final it is difficult to play like this the whole match. I am very, very happy."
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