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Arthur spent two seasons in the same side as Lionel Messi at Barca and is now relishing the prospect of playing alongside another multiple Ballon d'Or winner in Ronaldo.
"I have had the privilege of playing with great players. Playing with Ronaldo is almost the realisation of a dream," he said when presented to the media on Wednesday.
"Today is a very important day for me. I thank my family, the managers, Fabio Paratici, chief football officer and all those who have welcomed me."
Juventus won a ninth straight Scudetto last season but sacked head coach Maurizio Sarri after losing to Lyon in the last 16 of the Champions League.
Iconic former midfielder Andrea Pirlo was installed as Sarri's successor and Arthur is honoured to play under the Italian, who has never previously managed at senior level.
"I haven't talked to the coach in detail yet. But he played football in a unique way, different to others. I feel privileged to play for such a coach," he said.
"Anyone with an interest in football followed his playing career."
Arthur won two trophies in his two seasons at Camp Nou, but Barca fell short in the Champions League in both campaigns.
It has been 24 years since Juve last won silverware in Europe's premier club competition and Arthur is out to change that.
"One of the main reasons for joining was this," he said. "Here I can play with important players and the Juventus project is extremely ambitious.
"The Champions League is a priority. I will work with my team-mates to reach that goal and many others.
"We are talking about Juventus, a club with a unique history. It is a team with an important structure - all these factors will always make it unique."