The right-sided player, who will provide competition at full-back for veteran Dani Alves, completed his switch from Sao Paulo to last season's La Liga runners up on Tuesday.
Despite not being on the radar of most European football fans, the 24-year-old is hoping he can make the €5.5 million (£4.3m) deal look like a steal for Luis Enrique's men in 2014-15.
"This is the pinnacle for me," he told Barca's official website. "This is everything I could wish for. I am so happy to be able to represent this club.
"I want to thank everyone involved in me coming here and I just hope I can return their confidence in me by performing well on the pitch."
Douglas also admitted he is excited about playing alongside fellow Brazilian Neymar, who made the move from his homeland to Camp Nou a year ago, and hopes he can refine his own ability in Spain.
"I want to learn, because the style of play here is different to how we play in Brazil," he added.
"They are all big stars here. I've seen them play of course and I’ve played against Neymar in Brazil - he is a sensational player and a great representative for the Brazil team."