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.
