The 25-year-old playmaker, the world's third most expensive footballer after securing a long-desired transfer from Liverpool, will be officially presented to the world's media on Monday from 1130 GMT.
But in a club video message released on Sunday, Coutinho, who posed for photographers at the Camp Nou wearing a tracksuit top in the colours of the team, insisted: "I want to play, win trophies and make the supporters happy. Those are my objectives.
Coutinho has agreed a deal through to 2023 and is looking forward to playing alongside Messi, Luis Suarez and Andres Iniesta.
He described them as well as club stalwarts Gerard Pique and Sergio Busquets as "idols".
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Coutinho has already played alongside Suarez for 18 months at Liverpool before the Uruguayan made the same move to Spain in 2014.
"Everybody knows about his quality. He has been playing at the highest level for years now and that is important," said Suarez.
"Now we need to make sure he feels at home because we know that changing club is always difficult, but I think he is the type of player who will fit well into the team."
"Coutinho is a player who I think can bring a lot to us," said Valverde. "He's an important signing."
"I have seen him play in various positions -- on the right, the left, in the middle, on the wings. We will evaluate all of this...but, of course, I don't think he will play as a goalkeeper!"
- Blow for Liverpool -
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The swoop for Coutinho -- which contains a 400 million- euro release clause -- is the third biggest transfer in football history.
Rio-born Coutinho arrived at Liverpool from Inter Milan for a mere 8.5 million ($11.5 million) in January 2013 and scored 54 goals for the club in all competitions, although he won no silverware during his five-year stay at Anfield.
Barcelona had tried to sign Coutinho last summer and his departure is a blow to Liverpool as he had just returned to top form after an injury-hit start to the season, scoring seven goals in the last eight games of 2017 to put his side firmly in the Champions League places.
"Philippe was insistent with me, the owners and even his teammates this was a move he was desperate to make happen."
For Barcelona, Coutinho's signing allows the club to move on from the bitter experience of losing his Brazil teammate Neymar to Qatar-backed PSG.
Coutinho's age is also highly attractive to Barca with Messi, Suarez and Iniesta all in their thirties.
Liverpool have been tipped to quickly reinvest their windfall from the Coutinho sale.