The former defender is set to take over following the decision to sack Quique Setien in the wake of the 8-2 destruction by Bayern Munich in the UEFA Champions League quarter-final.
Koeman confirmed that discussions were underway with Barca. The Netherlands boss had a clause in his contract allowing him to leave for the job at Camp Nou, although a report in La Vanguardia suggests Barca will have to pay between €4million and €5m in compensation.
The 57-year-old was filmed leaving El Prat airport after he arrived by private jet, and he is now expected to sign his Barca contract in the coming hours.
Barcelona president Josep Bartomeu hopes the Dutchman can restore some lustre to a Barca dressing room reeling from a sorry end to a disappointing season.
"These days, everything comes out in the press," he said to Barca TV. "If nothing goes wrong, Koeman will be the coach we'll announce who will lead this team and these players forward, with a different project and with a coach who the fans know well, not only as a player but also as a coach.
"We're backing him because we know him really well in terms of how he is and how he thinks and how his teams play, but also because of his experience, for being in Johan Cruyff's 'Dream Team'. He knows Barca and the way to understand football."
Although he has resisted calls to step down, Bartomeu has brought forward elections to March next year, having already overseen the departures of Setien and Abidal.
A number of first-team players are expected to be moved on before the start of the 2020-2021 season, with club captain Lionel Messi reportedly eager to leave and experienced defender Gerard Pique having offered to depart for the good of the team.