Gray cited family responsibilities as the main reason for his decision, which will bring to an end his 14 year career at ICON. CFO Ciaran Murray will replace Gray and has also been appointed a memeber of the CRO's board.
Jefferies & Co analyst David Windley said the departure was "unexpected and seems to indicate that the decision was made in recent weeks."
He added that: "Murray will assume the CEO position at a critical time in the development of strategic partnerships. The reasons sound benign, but loss Mr. Gray's leadership leaves a significant hole to fill."