It is also understood that he was in discussions for a possible move to architect Hamilton Associates, but a deal to join the Chelsea-based practice fell through.
Industry sources have long been speculating about a rift between Shuttleworth and Foster. Reportedly, the two men fell out over Shuttleworth's Building interview in January, in which he discussed his personal role in the initial design of some of the practice's great buildings.
Sources have also suggested that there was a dispute about money. However, Shuttleworth denied this, saying: "Norman's been very generous."
Foster is understood to have tried to persuade Shuttleworth to stay, and in the event the departure was said to be amicable.
It has been a very difficult decision to leave lifelong friends and a profound part of my life
Shuttleworth said: "After nearly 30 years working with Norman Foster, I have decided to leave the practice and explore opportunities elsewhere. It has been a difficult decision to leave lifelong, very talented friends and what has been a very substantial and profound part of my life.
"I have been very fortunate to work on the design of some of the most innovative and high-profile buildings in the world. It has been a richly rewarding and deeply satisfying experience."
Foster said: "I want to personally say how much I have valued Ken's remarkable contributions over the years, to express my gratitude and wish him every success in the future."
Peter Rogers, director of developer Stanhope, said the reason for the departure was Shuttleworth's need to strike out on his own.