The Catalan club said, in an official statement, that it had reached an agreement with the player, after he terminated his contract with Chelsea.
He explained that Alonso will sign a contract until June 30, 2023, and the penalty clause will be 50 million euros.
Alonso will strengthen the defense of coach Xavi Hernandez's team, which also included Thursday right-back Hector Bellerin.
Alonso played for 6 seasons at Chelsea, after being active in the ranks of Bolton and Sunderland in the Premier League, and Fiorentina in the Italian League.
Barcelona worked hard to strengthen its ranks this summer, after a season in which it suffered from frequent setbacks, at the local and European levels./End of 9