The 58-year-old Portuguese, who won 25 trophies during his managerial career, was sacked by Premier League side Tottenham Hotspur in April after 17 months at the helm.
Mourinho will take over the Italian side ahead of the 2021-22 campaign, with a deal that will last until June 30, 2024.
“The incredible passion of the Roma fans convinced me to take the job and I can’t wait to start next season,” Mourinho said in a statement.
Roma announced on Tuesday that current coach Paulo Fonseca will step down at the end of the current campaign.
The club suffered a heavy 6-2 loss to Manchester United in the Europa League semi-final first leg last week and are currently in seventh place in the league.
“We are delighted and delighted to welcome José Mourinho to the AS Roma family,” Roma President Dan Friedkin and Vice President Ryan Friedkin said in a statement.
“A great champion who has won trophies at all levels, José will bring tremendous leadership and experience to our ambitious project.
“José’s appointment is an important step in building a long-term and consistent winning culture across the club.”
Mourinho is one of the best known and most successful coaches in the game and has coached players like Real Madrid, Manchester United, Inter Milan and Chelsea before.
This is the second time Mourinho has worked in Serie A. He coached Inter Milan between 2008-2010, in his last season, guiding the team to a remarkable hat-trick – Serie A title, la Coppa Italia and the Champions League.