The Catalan club took to social media to announce the news after a lengthy period of rumours circling.
Flick was president Joan Laporta's pick to replace Xavi, who officially departed the club he formerly skippered earlier today.
The 59-year-old won the Bundesliga twice with Bayern and led them to Champions League glory, while also winning the Club World Cup, European Super Cup, German Cup and German Super Cup along the way.
That was followed by a stint with the German national team in 2021, which was less successful.
Elimination from the group stage of the 2022 World Cup took its toll, and the following year Germany managed just three wins in 15 games as part of their Euro 2024 preparation.
In Barcelona, he takes over a team which finished second in La Liga behind Real Madrid.
The Blaugrana also lost the Spanish Super Cup to Los Blancos, fell in the quarter-finals of the Copa del Rey and at the same stage of the Champions League.
