The Frenchman has signed a five-year contract, with a buyout clause set at €300million.
La Blaugrana paid Lenglet's full €35m release clause after failing to negotiate a lower fee for the France global.
It brings to an end a saga that has stretched several months, with the Catalan side having always been linked with the Frenchman.
The French global is set to sign a five-year contract with the Catalans. The deal with Barcelona also includes a €300m release clause.
Do you think Lenglet will be a success at Barca if he joins?
Lenglet enjoyed a productive spell at Sevilla, making over 70 appearances and scoring four goals for the club. He has played for France at Under-21 level but has never been called up to the first team.
Lenglet, a former France under-21 worldwide, becomes Barca's second signing of the summer following confirmation last week that Gremio midfielder Arthur Melo will also join the club this month.
He becomes the second new arrival of the week after Arthur.