Mourinho was fired by English Premier League club Tottenham last month and is returning to Italy, where he led Inter Milan to league and European success.
“The club are delighted to announce an agreement has been reached with José Mourinho for him to become our new head coach ahead of the 2021-22 season,” Roma announced.
Mourinho will replace another Portuguese, Paulo Fonseca, who it was already announced, would leave his role at the end of the season.
Roma currently sit seventh in Serie A.