The Argentina midfielder will have to vie for playing time with Spain trio Xavi, Sergio Busquets and Andres Iniesta at the heart of Pep Guardiola's side, after signing a four-year contract with the Spanish champions.
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"It would be stupid to think I would come here and be playing every game," Mascherano said at his presentation in the Nou Camp.
"You have to respect the people who are already doing well and who have won everything. In the positions I play in, there are three world champions.
"It will be a honour to be able learn from them and to grow with them."
Barca's sporting vice-president Josep Maria Bartomeu said the player had taken a pay cut to help complete the move, and said Mascherano's arrival would be their last of the current transfer window.
The 26-year-old passed a medical earlier in the day before signing his contract, which has a buy-out clause of 90 million euros.
Spanish media reported he moved for around 22 million euros.
Mascherano became Barca's third acquisition of the summer after Spain striker David Villa and Brazilian full-back Adriano Correia, and he helps fill the gap left by Yaya Toure's departure to Manchester City.
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