Brazilian defender Douglas has signed a five-year deal with Barcelona for a fee of £3.2 million from Sao Paulo.
The fee could rise to £4.4 million depending on the number of games he plays.
The deal was agreed earlier this week and, after passing a medical, Douglas was able to put pen to paper.
The 24-year-old could be Barcelona’s last signing for a while as the club face a FIFA-imposed transfer embargo for the next two transfer windows.
Barcelona will be barred from signing players until January 2016 after FIFA rejected an appeal against their transfer ban, imposed in relation "to the protection of minors".
FIFA imposed a 14-month ban on Barcelona in April this year after the club were found to have breached rules on the signing of international players under the age of 18.
The club are appealing at the Court of Arbitration for Sport, but are allowed to bring players in during this transfer window.