Local media reported that the move to Al Hilal came after Benzema rejected an offer to extend his contract with Al Ittihad. The former France international striker had missed the team’s previous two league matches.
"Al Hilal signed French star Karim Benzema on a free transfer to represent the football team for one and a half years," the Saudi club said in a statement.
Benzema had a successful spell with the Jeddah-based Al Ittihad, leading them to the league title and the King's Cup last season. It was the first domestic double in Al Ittihad's history.
"This journey gave me a lot, both personally and professionally," Benzema, who joined Al Ittihad on a free transfer in 2023 after 14 years with Real Madrid, said on X.
"I leave with my head held high, proud to have worn these colours and of everything we shared."
The former Real Madrid striker, 38, scored 16 goals in 21 matches for Al-Ittihad in all competitions this season.
Al Hilal sit top of the league standings with 47 points, one point ahead of Cristiano Ronaldo's Al Nassr. Al Ittihad are sixth with 34 points.