Neymar signed a five-year contract with club president Sandro Rosell after choosing Barcelona over Real Madrid.
The 21-year-old jogged onto the Camp Nou field for the first time in his new Barcelona jersey with "Neymar Jr" on the back.
"I am very happy, very moved to be a Barcelona player and fulfill my dream," Neymar told the crowd of 56,500 that welcomed him. "I have come to add my part so that Lionel Messi continues to be the best player in the world."
Barcelona vice president Josep Bartomeu said that the transfer cost Barcelona 57 million euros ($74 million), to be split among Santos and three other companies that own shares of the player's rights. Bartomeu said the club had expected to pay about 40 million euros, but that "the interference of other clubs" inflated the price, an allusion to Real Madrid.
Barcelona's most expensive transfer had been for Zlatan Ibrahimovic in 2009, when it gave Inter Milan 45 million euros (then $64 million) plus forward Samuel Eto'o.
Neymar led Santos on its greatest run since Pele left to sign with the New York Cosmos after the 1974 season. Neymar helped Santos win the 2010 Brazilian Cup, the 2011 Copa Libertadores and three straight Sao Paulo state championships, becoming the team's leading scorer in the post-Pele era with 138 goals in 230 matches.
Neymar's flight from Brazil arrived an hour behind schedule at about 1 p.m. local time. Decked out in black with sunglasses and a baseball cap, he took a chartered bus straight to Camp Nou.
"He can bring us a lot because he is very talented player," Barcelona midfielder Andres Iniesta said. "He brings his ability to break down defenses, to score, and to entertain. He is young. He has a long path ahead of him, and he is coming to the best place to grow ... Leo will be make Neymar better, and Neymar will make Leo better."
Brazilian right back Dani Alves recalled other Brazilian forwards who have thrived at Barcelona, including Romario, Ronaldo, Rivaldo and Ronaldinho.
"He will give us a Brazilian touch," Dani Alves said. "The others left their mark. I am sure he will, too."
Neymar flew to the Mediterranean city on a private jet with a small entourage, including his father Neymar Silva Santos.