The Premier League leaders confirmed the signing tuesday. It is a club-record signing for £57 million.
The 23-year-old has signed a contract until 2023.
Laporte, who made 222 appearances for Athletic, will wear the number 14 shirt at City.
«I am very happy to be here,» he said to the clubs official site.
«City are a club with a lot of ambition and they are one of the best teams in Europe.»