The Brazilian club announced last week that the right-back was bound for Camp Nou and the Blaugrana have now confirmed the 24-year-old's imminent arrival in Catalunya.
"FC Barcelona and Sao Paulo FC have reached an agreement in principle for the transfer of the player Douglas Pereira," read a statement on the Liga side's official website.
"The cost of operation is €4 million plus €1.5m in variables that are dependent upon games played.
"Douglas will travel to Barcelona later this week to undergo a medical. He will sign a contract with FC Barcelona for the next five seasons."
Sao Paulo president Carlos Migue Aidar admitted that he was sad to be losing Douglas and that the deal had been complicated by third-party ownership.
"This is not a moment of joy, as we are losing one of our starters, but now he will be able to play at the Champions League," he stated.
"We wish the player all the happiness, and that he may have a great spell in Spain. And who knows, maybe Sao Paulo can count on him again in a couple of years.
"It was a complicated deal, as the club had a third party involved, but, ultimately, Sao Paulo managed to get €3.6m for its 60 per cent share on the player's rights, as it should."
Douglas, who has never been capped at senior level by Brazil, becomes Barca's fifth high-profile defensive acquisition of the summer, with Claudio Bravo, Marc-Andre ter Stegen, Thomas Vermaelen and Jeremy Mathieu already having arrived at Camp Nou.