According to transfer specialist Fabrizio Romano, the two clubs have agreed on a deal worth 22 million euros, with a further nine million euros available through performance-related bonuses.
The add-ons are expected to be linked to appearances and Barcelona's success in domestic and European competitions.
Adeyemi is set to sign a contract until 2031 after deciding not to extend his stay at Borussia Dortmund. With just one year remaining on his current deal, the Bundesliga club opted to cash in on the 24-year-old this summer.
The winger joined Dortmund from RB Salzburg in 2022 in a deal worth 30 million euros and has established himself as one of the club's quickest attacking players.
Sky Germany reported that Adeyemi will earn around six million euros per season at Barcelona, while Dortmund have also negotiated a 35 per cent sell-on clause as part of the agreement.
Thibaut Courtois has revealed he is prepared to continue playing for Belgium but wants to take a break from international duty during the upcoming UEFA Nations League campaign to focus on his fitness.
Barcelona president Joan Laporta has welcomed the club's move for Karim Adeyemi, saying everyone at the club is excited about bringing the Germany international winger to Camp Nou.
In-demand forward Karim Adeyemi has been granted permission to open talks with Barcelona after Borussia Dortmund accepted a bid believed to be in the region of 30 million euros.
Barcelona are approaching a pivotal stage in determining Ferran Torres' future, with the Spain international attracting interest from Paris Saint-Germain while his contract situation is unclear.
