That is according to transfer expert Fabrizio Romano.
Vidal was deemed surplus to requirements by Bayern Munich following an evaluation of the squad by new manager Niko Kovac.
Manchester United were linked with the 31-year-old, who struggled with injury last season and had entered the final year of his Bayern contract.
Inter Milan were understood to be the frontrunners for Vidal’s signature but after stealing Malcom from under the noses of Roma, Barcelona appear to have hijacked another deal.
Romano wrote on Twitter: “Vidal to Barcelona until 2021, Monday presentation at the Camp Nou.”
Vidal will form a formidable but ageing Barcelona midfield with Sergio Busquets and Ivan Rakitic.
European deadline days
August 9
England – Premier League and Football League
August 31
Austria, Belgium, Croatia, Denmark, France, Germany, Greece, Hungary, Northern Ireland, Poland, Russia, Scotland, Serbia, Spain, Turkey, Ukraine, Wales
September 1
Armenia, Burkina Faso
September 3
Romania
September 5
Mexico
September 6
Bulgaria, Slovakia
September 8
Czech Republic
September 21
Portugal