Villa have the option to buy the Brazil international, who is now expected to travel to Birmingham to complete the formalities of his move.
The midfielder will link up with Villa boss Steven Gerrard, who he played with at Liverpool from 2013-15.
"Aston Villa and FC Barcelona have agreed terms for Philippe Coutinho to spend the rest of this season on loan at Villa Park," Villa said.
"The agreement, which is subject to the player completing a medical and receiving a work permit, also includes an option to buy and Philippe will travel to Birmingham in the next 48 hours."
Villa are 13th in the Premier League after three defeats in four games following a bright start under Gerrard, who took over at Villa Park in November.
Gerrard on Thursday described his former Liverpool teammate as a "special footballer" while refusing to comment on speculation linking him with a move to Villa.
Barcelona said in a statement that Coutinho, who has made 106 appearances for the club, was expected to travel to Birmingham in the next few hours.
Coutinho has struggled to establish himself as an automatic choice in his four years at Camp Nou after signing from Liverpool for €135 million.
He has made just 12 La Liga appearances this season, scoring two goals as Barca languish in fifth place, 15 points behind leaders Real Madrid.
It is the second time the 29-year-old Brazil playmaker has been loaned out by Barcelona having spent the 2019/20 season at Bayern Munich, who he helped to win the Champions League, knocking out his parent club en route to the title.
Villa next face Manchester United on Monday in the FA Cup third round.