The 24 year-old joins Girona on a contract to 2029.
He arrives from SC Braga for €8.5m plus the transfer of Gabri Martínez.
The winger, who serves to make the arrival of Abel Ruiz cheaper since his price was close to €12m, goes the other way and will sign for the Portuguese team. Girona will also retain a percentage of a future sale.
Ruiz said, "First, I want to thank the opportunity that has been given to me. I am very happy to be here and now I want to enjoy the experience. For me it was a dream to return to the Spanish League and to a club like Girona, which has had some very good years. I am coming to try to make the club grow.
"There was already some contact since last season. I have been talking to him (coach Michel) and he has shown interest in me. Since last year I had already had in mind to come here.”