“I wish them every success. I believe they have the right attributes to create history by lifting the World Cup in July and winning the Ashes that follows it.
“There is never a great time to leave an international set-up and despite what will be a fantastic summer for English cricket, the opportunity to shape the future of one of the game’s biggest counties was too much to resist.
“It would have been tough for me to have turned down the opportunity once Warwickshire showed an interest in me.”
Giles, who must now decide whether to appoint a short-term replacement before the appointment of a new head coach, paid tribute to Farbrace.
“I would like to thank Paul for all his efforts over the last five years as a key figure in England’s success across the red and white ball formats,” he said.
“Paul was integral, alongside, Andrew Strauss, Trevor Bayliss and Eoin Morgan, in transforming our white-ball strategy, which has seen us become the best team in the world leading into a World Cup year.
“I will now start the process to find a successor and work closely with our existing set-up to ensure we have everything in place ahead of a busy summer of international cricket.”