Laporte has signed a five-year contract at the Etihad after City agreed to meet his £57m release clause on Monday.
The 23-year-old becomes the most-expensive player in the club’s history, surpassing Kevin De Bruyne, who cost £55m from Wolfsburg in 2015.
Laporte told the club’s official 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.”
City have lacked depth in the centre of defence all season, with just Nicolas Otamendi and John Stones consistently fit and trusted by Pep Guardiola.
Vincent Kompany’s long-standing injury problems have prevented him from playing more regularly, while doubts remain over the ability of Eliaquim Mangala.
Laporte, who is yet to be capped by France at international level, previously rejected the chance to work with Guardiola at City in the summer of 2016, electing to sign a new contract at Athletic.
The defender's decision frustrated City at the time but a year-and-a-half later, they have renewed their interest in Laporte and found him more willing to leave Bilbao.
Laporte's arrival brings City's spending on defenders since the end of last season north of £220m, following the arrivals of Benjamin Mendy, Kyle Walker, Danilo and goalkeeper Ederson in the summer.
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