• The Portuguese manager will replace Paulo Fonseca, who Roma announced earlier on Tuesday would leave the club at the end of the current campaign.
• Mourinho was sacked as Tottenham boss on 19 April and had said he would "wait to be back in football" following his dismissal.
Jose Mourinho has been appointed Roma manager from the start of the 2021-22 season.
The 58-year-old will replace fellow Portuguese Paulo Fonseca, who Roma announced earlier on Tuesday would leave at the end of the current season.
Mourinho was sacked as Tottenham Hotspur boss on 19 April and had said he would "wait to be back in football" following his dismissal.
He has signed a three-year deal with Roma, who are seventh in Serie A.
"Thank you to the Friedkin family for choosing me to lead this great club and to be part of their vision," said Mourinho, who has also managed Inter Milan, Chelsea, Manchester United and Real Madrid outside his homeland.
"After meetings with the ownership and Tiago Pinto, I immediately understood the full extent of their ambitions. It is the same ambition and drive that has always motivated me and together we want to build a winning project.
"The incredible passion of the Roma fans convinced me to accept the job and I cannot wait to start next season."
Mourinho was dismissed after 17 months in charge of Spurs following a poor second half of the season in which they slipped from top of the table to outside the European places.
This season Mourinho suffered 10 league defeats in a single campaign for the first time in his managerial career.