Aymeric Laporte has completed his club record move from Athletic Bilbao to Manchester City, the Premier League club have announced.
The 23-year-old defender had been in discussions with City after Bilbao confirmed on Monday that his buy-out clause, believed to be around £57million, had been paid.
Laporte, a France Under-21 international, has signed a five-year contract to play under Pep Guardiola at the Etihad Stadium.
Laporte told the club's website: "I am very happy to be here. City are a club with a lot of ambition and they are one of the best teams in Europe.
"I am looking forward to working under Pep Guardiola and trying to help the club to achieve success.
"It means a lot that the club have shown faith in me and I am excited to get started."
The fee eclipses the £54million City paid for Kevin De Bruyne in 2015 and also makes him the second-most expensive defender in the world after Liverpool's £75million signing Virgil van Dijk.
John Stones and Nicolas Otamendi have formed a strong central defensive partnership this season but the area was still identified as a problem position.
Vincent Kompany's recurring fitness issues and the inconsistency of Eliaquim Mangala led to City, who were also linked with West Brom's Jonny Evans, seeking reinforcements.
Pep Guardiola says that Laporte is ready to play straight away but may need time to adapt to the Premier League.
"He's fit, he's been playing the last period," Guardiola said in a press conference. "Of course he has to adapt because the Premier League is special in many senses.
"He is intelligent, he will read what is the situation. Even for English players, when they come into the Premier League it's always a little bit tough. We will be patient because he doesn't come for three months, he comes for five years."
City director of football Txiki Begiristain said: "We are delighted to have signed Aymeric.
"We have assessed defensive options and he is a player we have admired for a long time.
"With his quality and ability to play out from the back, we feel Aymeric will fit in perfectly with Pep Guardiola's playing style."