Ex-Liverpool ace Mascherano: Barcelona move chance of a lifetime
Mascherano was unveiled to the fans at the Nou Camp and then spoke to the press, where the Argentina international could not hide his delight at joining the Pep Guardiola's hugely-successful side.
"When I landed I said that I was achieving a dream. At last I will be able to say that I play for Barcelona, the team who I wanted to play for," said the 26-year-old, who has reportedly cost Barca 22million euros (£18million) and whose contract has a buy-out clause of 90million euros.
Mascherano knows he has a fight on his hands to get in Barca's starting line-up though, with Guardiola having eight of Spain's World Cup-winning squad to choose from as well as the likes of Lionel Messi, Dani Alves and Seydou Keita.
"It would be stupid if I thought I was going to play all the time. You need to respect the people here who have been doing so well," he added. "In my position there are three world champions who have won everything (Xavi, Sergio Busquets and Andres Iniesta).
"For me it is a dream to grow, learn and enjoy playing next to them."
He added: "I know that they've won everything, it's a team full of great players, with a base of world champions and I will try to be humble and help the team continue winning things. I'm going to have the chance to play with players who I admire and I will able to say that I've grown and that I've been a better player at this club.
"This is an opportunity of a lifetime. I will train to be ready when I'm needed."
Mascherano also insisted he is not a like-for-like replacement for fellow midfielder Yaya Toure, who recently left Barca for Manchester City in a big-money move.
"Toure is a great player, he has left his mark on this club. I've not come to replace him, but to do my job the best that I can," said Mascherano, who will wear the number 14 shirt vacated by Thierry Henry this summer.
"They've signed me for what I've done in the last few years. I'm not going to try and be similar to Toure, because I'm not. But I can give different things, neither better or worse, but different.
"I'm a defensive player, but I can contribute other things. In my career I've played in other positions and whatever I'm needed to do I'll do it. The coach will decide."