Roma will be obliged to make Perez's transfer permanent for an initial €11m – with a further €4.5m attached to performance-related clauses – if "certain sporting targets" are achieved.
Should the Serie A giants be required to stump up that cash, the 21-year-old winger, who struggled for consistent game time at Barca under Ernesto Valverde and then Quique Setien, will join on a contract until June 2024.
✅ Official: Carles Perez is now a Roma player!— AS Roma English (@ASRomaEN) January 30, 2020
Even one missing child is one too many. #ASRoma have teamed up with organisations around the world to help the search – including for the seven youngsters featured here. 🌍 pic.twitter.com/4W33XKVhUF
"I know I am leaving a great club like Barcelona, but I'm joining another great club in Roma," said Perez. "I'm really happy and I can't wait to start training alongside my new team-mates."
Roma chief executive Guido Fienga said: "We are hugely satisfied with Carles' arrival in Rome. Carles learned his trade in one of the best youth academies in Europe and has been playing for a club with so much talent at its disposal.
"We are all hopeful that he can immediately have a significant role to play within our squad."
Perez's departure from Barca - who retain the right of first refusal on any potential future sale - does not necessarily mean there will be any new arrivals at Camp Nou, with Quique Setien stating on Wednesday he was happy with the squad at his disposal.
Roma also announced the signing of Gonzalo Villar from Elche for an initial €4m, with the midfielder putting pen to paper on a four-and-a-half-year deal.
"My first impressions are all great. I'm joining a massive club, one of the best in Italian football. I'm really happy right now," Villar told Roma TV.
"It'll be a great challenge for me. I'm coming to a new country, a beautiful country. I can't wait to get started with my team-mates and to show what I am capable of doing.
"I spoke to the coach [Paulo Fonseca], who told me the confidence he has in me. He told me that he likes the way I play on the pitch, but that I need to work hard to adapt to this new challenge.
"He made a strong impression and I'm confident he'll be a great coach for me."