Barca appointed Xavi as their new manager on Friday to replace Ronald Koeman on a two-and-a-half-year deal.
The former midfielder, who spent 17 years in the Barcelona first team between 1998 and 2015, joined from Qatari outfit Al Sadd after the two clubs agreed on the payment of a release clause in his contract.
Fallen giants Barca are currently ninth in La Liga, 11 points adrift of leaders Real Sociedad and 10 behind arch-rivals Real Madrid.
At his official unveiling in front of almost 10,000 fans at the Nou Camp, Xavi said: “I am very excited. I want to thank the club and everyone here. You have given me goosebumps.
“I just want to say one thing. We are the best club in the world and we will work hard to achieve success. We can’t afford to draw or lose. We are Barca and we have to win every game.
“We need you (the fans) especially through bad times. We are in a difficult situation as a club, but now we have to think only about what’s good for Barca.”
Club president Joan Laporta joined Xavi on the pitch and said: “Today is a day that will go down in club history.”
Xavi’s first match in charge will be the derby against Espanyol on 20 November, after the international break.