Jules Kounde of France will join Barcelona from Sevilla on a five-year deal with a 1 billion euro (£837 million) buyout clause.
The reported transfer fee for Kounde, who has 11 France caps, is 50 million euros (£41.85 million).
The 23-year-old joined Sevilla from Bordeaux in 2019 and made 133 appearances, winning the Europa League in his debut campaign.
Kounde is Barcelona's fifth summer acquisition and is also desired by Chelsea.
The defender joins the Nou Camp after the Catalan club acquired Brazilian winger Raphinha from Leeds in a £55 million deal and Poland striker Robert Lewandowski for £42.6 million from Bayern Munich.