The 19-year-old playmaker returns to his native Catalonia after signing a contract which includes a 12 million-euro release clause.
The first signing by Barcelona under new head coach Tito Vilanova’s reign is expected to join up with Barca’s B team.
“Being in England for three years has helped me to mature a lot and to become physically stronger,” Roman said in a statement on the club’s official website. “I’m raring to start and start learning.
“When I heard Barca were interested in me, that was my priority. I can assure you that I’ll work hard and give everything I can out on the pitch.”
Roman arrived at City from Espanyol as a 16-year-old and played all of his football for the club at youth level and with the Elite Development Squad. Although he was named on the bench for the first team last season, he never made a senior appearance for the recently-crowned Premier League champions.
Despite that the versatile midfielder was highly rated following his performances for City’s reserves.