The Premier League club announced on Tuesday evening that the formalities of the transfer, which includes an option to buy, had now been processed.
"Philippe Coutinho arrived at Bodymoor Heath on Tuesday afternoon to complete his move to Aston Villa," a club statement read.
"The Brazil international, 29, travelled straight to the club's training complex having landed in Birmingham, coming after he successfully completed his medical and obtained a work permit.
"Coutinho will spend the rest of this season on loan at Villa Park from FC Barcelona, with the agreement including an option to buy."
Coutinho, who also had spells at Inter Milan and Bayern Munich, cannot wait to link up with his new club, where former Liverpool team-mate Steven Gerrard is now head coach.
"It's a pleasure to be here; it's a great club," the Brazilian told the club's official website.
"I spoke a lot with the manager, with Stevie, and he told me about the club and his ambitions. I'm very happy to be here and I'm looking to enjoy my football.
"I've known Stevie for a long time. I played with him and I learned a lot from him.
"He's someone who I have big admiration for. I hope to do my best here. For sure, I will work hard, and I hope together we can do good work."
Coutinho, who could make his debut in Saturday's Premier League clash with Manchester United at Villa Park is confident he can again make a big impression on the Premier League.
"I'm looking forward to meeting the fans, to being on the pitch. I know and I feel that they're happy that I'm here," he said.
"I want to repay that on the pitch and enjoy my football. I'm looking forward to being on the pitch.
"I always want to be at my best, doing my work. That's what I work hard for every day. I hope it will be a great rest of the season here."