The 23-year-old moved to Seville from Nancy last summer, and impressed during his first season in Spain - scoring four times in 54 appearances in all competitions.
Manchester United were also linked with the Frenchman earlier this summer, but Barcelona have won the race.
Earlier this month, it was reported that the Spanish champions were attempting to negotiate a deal for Lenglet as they were not prepared to pay his full release clause of £31.7m.
However, in a statement, Barcelona confirmed that they have met the buy-out figure in the centre-back's Sevilla deal.
"FC Barcelona has paid the buy-out clause for Clement Lenglet who is no longer a Sevilla FC player," read a statement on the Catalan club's official website.
Lenglet's five-year contract at Camp Nou includes a release clause of £265m.