The right-back joins from Tottenham on a five-year deal and has opted to take the number two shirt.
He becomes City’s third signing of the summer, following in the footsteps of Bernardo Silva and Ederson.
“I am thrilled to be signing for City and can’t wait to get started,” Walker said. “Pep Guardiola is one of the most respected managers in the world and I feel he can help me take my game to a new level.”
The England right-back, 28, became a priority target following Dani Alves’ snub for Paris Saint-Germain.