The Giallorossi have won just one of their last six Serie A games and were recently knocked out of the Coppa Italia by city rivals Lazio, where Mourinho was sent off.
Following that defeat, Mourinho likened himself to fictional wizard Harry Potter, saying his position at the club was raising fans’ expectations for success.
They are 22 points behind league leaders Inter Milan.
The 60-year-old joined Roma in 2021 and spent two-and-a-half years in the role, leading them to the Europa Conference League title in 2022.
He also guided them to the Europa League final last season, where they were defeated by Sevilla on penalties. His contract was due to expire in June.
A club statement read: “We would like to thank Jose on behalf of all of us at AS Roma for his passion and efforts since his arrival at the club.
“We will always have great memories of his tenure at Roma, but we believe that an immediate change is in the best interests of the club.
“We wish Jose and his assistants all the best in their future endeavours.”
Roma next host 18th-placed Verona on Saturday.