The 17-year-old, considered among his country's brightest prospects, has made only a handful of professional appearances so far, having made his debut less than a year ago for Brazilian club Vasco Da Gama.
"Leverkusen have an outstanding reputation in my country and everyone knows the club in Europe as one where many Brazilian players have been happy here," he said in a club statement.
"I think it important to take the next step abroad after careful thinking and that is why I decided in favour of a club that is serious and still sets big goals."
A versatile winger, Paulinho also helped Brazil to a third-place finish in the Under-17 World Cup last year and had sparked the interest of a string of top clubs, including in Spain, England and France.
He is currently recovering from a broken arm suffered earlier this month.
Leverkusen are in fourth place in the Bundesliga with three games remaining and are in contention for a Champions League group stage spot, with the top four teams qualifying automatically.
(Reporting by Karolos Grohmann; Editing by Toby Davis)
