The 30-year-old left Real Madrid this summer after his contract with the European champions expired.
Isco spent nine years with Real Madrid, whom he joined from Malaga in the summer of 2013 and won among other honours five UEFA Champions League trophies, three La Liga titles, one Copa del Rey and three UEFA Super Cups.
The Valencia youth product made 353 appearances in total for Los Blancos, scoring 53 goals and laying on another 56 assists for his teammates.
He fell out of favour under Carlo Ancelotti last season, only making 14 La Liga appearances.
After finding his new home in Seville, Isco is determined to prove his doubters wrong by getting back to his old self.
"I want to show the level that I have and that I have never lost. It's normal for there to be doubts, but I'll take care of dispelling them," Isco told Sevilla's media channels after signing his two-year deal.
"It has been a difficult summer, different. I've had too many vacations, I've taken advantage of them to get in shape and now I can't wait to play again, which I haven't done for a while.
"I'm not complaining, I've been lucky because I've played for big clubs and I've won almost everything, but I don't like to think too much about the past but about what's to come."
Isco also expressed delight to be reuniting with manager Julen Lopetegui, whom he worked with briefly at Real Madrid and also at the Spanish national team.
"He has always trusted me and I like his football, what he proposes. It is a football that is more suitable for my style," he added.
"I thank him for his confidence, which for a footballer is paramount. The confidence he has given me, it has always been the maximum. Now it's up to me to restore his confidence on the pitch and show him that he's not wrong."
