The 57-year-old Dutchman, who spent six years at Camp Nou as a player, will leave the position of Dutch national team starter to upgrade to Quique Setien after his departure on Friday.
A on the official online website of the club said: “FC Barcelona and Ronald Koeman have reached an agreement for the Dutchman to take over as first-team coach until 30 June 2022.”
Barca’s president, Josep Maria Bartomeu, had in the past shown the club’s goal of appointing former Southampton and Everton coach after Setien’s dismissal.
Setien and director Eric Abidal passed through LaLiga after the humiliating 8-2 Champions League quarter-final loss to Bayern Munich.
Koeman signed a four-and-a-half-year contract when he replaced Dick Advocaat as head of the National in February 2018.
He will be the third driver this year, and Setién will replace Ernesto Valverde in January.
The club, which mocked confirmation by posting a video of Koeman noting the purpose of the victory in the additional time of the 1992 European Cup final on their Twitter account, also announced that Ramon Planes would upgrade to Abidal.
Koeman will inherit a team that ended in the rival real Madrid moment in La Liga with five issues separating the teams.
Barca failed to win a trophy in the primaries this season for the first time since 2013-14 and won the Champions League for the last time in 2015, Luis Enrique.
Koeman played 350 games as a defence for Barca and scored 106 goals after winning in his home country with FC Groningen, Ajax and PSV Eindhoven.
In addition to the European Cup, his honours in Spain included 4 league titles, a Copa del Rey, 3 Spanish Super Cups and a European Super Cup.
He has already controlled Valencia in Spain.
Koeman said the opportunity to train Barcelona was to turn down.
“Everyone knows that Barcelona is the club of my dreams,” he told the Dutch federation’s website. “It’s very special for me to have a coach there.
“It is an honor to be the national coach of the Netherlands. For the more than two and a half years, I’ve done everything I can to succeed.
“I look back proudly for what we have completed in combination with this period. The Dutch national team has a bright future, I am convinced.”
The governing body’s director of professional football, Eric Gudde, said, “We, Ronald’s resolution, respect your choice.”