The Ivory Coast international is believed to have turned down a host of clubs, including ones from the Premier League, to join Barcelona on a free transfer last summer following the expiration of his deal at AC Milan.
Kessie featured on 43 occasions for Xavi's side during the 2022-23 campaign, scoring three goals and registering three assists in the process, but he found it difficult to secure regular starts.
There has been a host of speculation surrounding the 26-year-old's future this summer, with a return to Italy thought to be a possibility, while there has also been suggestions of English interest.
However, it has now been confirmed that the midfielder has become the latest high-profile name to make the move to Saudi Arabia, with Al-Ahli securing his signature.
Barcelona have received a €12.5m (£10.8m) fee for a player who arrived on a free transfer, while his large wage packet has also been removed from the budget.
"FC Barcelona and Al-Ahli SC have agreed on a 12.5 million euro transfer for the player Franck Kessie," read a statement on the Catalan outfit's official website.
"FC Barcelona want to take this opportunity to publicly thank Franck for his commitment and dedication, and to wish him all the best and every success in the future."
Al-Ahli won the First Division League last season to secure a return to the top flight of Saudi Arabian football.
Matthias Jaissle's side have also added Riyad Mahrez, Allan Saint-Maximin, Edouard Mendy and Roberto Firmino to their squad during a standout transfer market.
Barcelona have brought in Oriol Romeu, Ilkay Gundogan and Inigo Martinez this summer to boost their squad, meanwhile, but they are still active in the market despite their financial issues.
Xavi's side are currently preparing for their 2023-24 La Liga opener against Getafe on Sunday night.