The 21-year-old, who is just under five years younger than Messi, will line up with the Argentine in a fearsome Barca attack next season after the Spanish champions beat arch-rivals Real Madrid in the race to lure him from Santos.
After passing medical tests and penning a deal that ties him to Barca until June 2018, Neymar told the almost 60,000 fans who had turned up to welcome him at the Nou Camp stadium that playing for the club was a dream come true.
"Barca is more than a club and a great team and I want to contribute to Messi staying the best for many years," he said.
At a later news conference, he told reporters jamming the press room he had struggled to fight back the tears when he had walked out on to the pitch.
"It is a great day for me and my family," he said.
"Having the chance to play with so many important players whom I have admired since I was a child is something I have to thank god for.
"I have never been concerned about winning the Ballon d'Or or being the best player in the world.
"The best player is already here and that's Messi. And now I can see him from close up and help him."
Neymar was accompanied by Barca vice president Josep Maria Bartomeu and sporting director Andoni Zubizarreta and Bartomeu revealed that Barca had paid 57 million euros to sign Neymar.
His contract included a buyout clause worth 190 million euros, he added.
Quizzed about the complex ownership structure of rights to the player, Bartomeu said there was a confidentiality agreement in place that prevented him revealing how much Barca paid to each of the four parties who held a stake to secure the rights.
Local media reported the four were Neymar's previous club Santos, investment firms DIS and Terceira Estrela Investimentos and an unidentified sports consultant.
Barca had not wanted to pay more than 40 million euros in total but the price had been forced up by the interest of Real and other clubs, Bartomeu said.
"He is one of the world's best talents of his generation and he could be a reference point," Zubizarreta told reporters.
"We will enjoy some magical nights with him and his team-mates," added the former Barca and Spain goalkeeper. "They will be delighted to share a dressing room with Neymar."
Barca are hoping the addition of the Brazilian will help them maintain their edge over Real in La Liga next season and propel them to a third European crown in six years.
