Sir James Bevan has been High Commissioner to India since 2011 but leaves on 30th November to join the Environment Agency.
He succeeds Paul Leinster, who retired last week after 17 years at the Environment Agency and seven as chief executive.
Sir Philip Dilley, chairman of the Environment Agency, said: “Sir James will lead the organisation with passion, energy and a clear commitment to continue the great work it does to protect and improve the environment and make it a better place for people and wildlife.”
Sir James Bevan said: “One of the biggest challenges of our time is protecting the environment and promoting growth. We need to do both, and I look forward to playing my part in that. The Environment Agency is a great organisation which makes a great contribution to our country. It will be an honour and a privilege to lead it."