The transfer fee is reportedly £142m, meaning that the Brazilian is set to become the second most expensive player of all time behind compatriot Neymar.
“The player will sign a contract for the remainder of the season and five more, and will have a buyout clause of 400 million euros,” read a statement from Barcelona.
Meanwhile, Liverpool manager Jürgen Klopp told Liverpool’s official club website, liverpoolfc.com: “It is with great reluctance that we – as a team and club – prepare to say farewell to a good friend, a wonderful person and a fantastic player in Philippe Coutinho.
“It is no secret that Philippe has wanted this move to happen since July, when Barcelona first made their interest known.
“Philippe was insistent with me, the owners and even his teammates this was a move he was desperate to make happen.
“Despite that, we managed to keep the player here beyond the summer window, hoping that we would be able to persuade him to stay and be part of what we are looking to do.
“I can tell the Liverpool supporters that we, as a club, have done everything within our means to convince Philippe that remaining part of LFC was as attractive as moving to Spain, but he is 100 per cent certain his future – and that of his family – belongs at Barcelona. It is his dream and I am now convinced there is nothing left at our disposal to change his mind.”
Klopp praised Coutinho for remaining “dedicated and committed” to Liverpool, but reminded supporters that the Reds had survived the departures of similarly important players before.
“You cannot transfer the heart and soul of Liverpool Football Club, although I am sure there are many clubs who would like to buy it,” he said.
Coutinho arrived at Liverpool from Inter Milan in the January 2013 transfer window and has since netted 54 goals in 201 appearances. However, he has not won a trophy with the Reds.
He will be hoping to follow in the footsteps of Luis Suárez, who left the Reds after the 2013/14 season and won a treble in his first year at the Blaugrana.