The Brazilian, who has been with Chinese Super League club Guangzhou Evergrande since 2015, has been a target for the Nou Camp club for much of the summer and has now completed his move.
Barca opened with an offer of £17million in July but have since significantly increased their offer for the 29-year-old to complete the deal.
It marks a return to European football for a player who spent two seasons at White Hart Lane, without hitting the heights expected of him following a £17 million switch from Corinthians.
He played 67 times for Spurs during those two seasons, scoring 11 times, but was eventually sold for a fee of around £10million as he headed to China in the summer of 2015.
Speaking at the start of July, at a time when he thought his move was close, the Brazilian revealed his excitement regarding the switch.
He told Mundo Deportivo: 'It is a unique opportunity for me to be able to play for Barcelona, the best team in the world and surrounded by the best players.
'I have to talk to my president, since I got the proposal I have not stopped thinking about it and I am waiting for everything to be resolved this week.'
Paulinho's arrival comes at a time when Barcelona are rebuilding following Neymar's departure to Paris Saint-Germain, with Liverpool's Philippe Coutinho their primary target to replace the Brazilian forward.
Coutinho put in a formal transfer request on Friday, just minutes after Liverpool insisted he was not for sale after rejecting an offer of £90m.