"Dave has an incredible track record of leading and growing successful technology companies, and his guidance on our board of directors has been invaluable," said Ashar Aziz, FireEye founder, CTO and former CEO.
"The combination of his leadership, operational experience, and industry expertise will without a doubt help usher FireEye into the next stage of its growth and expansion on a global scale.
"We welcome him to the leadership team."
Mr DeWalt has been chairman of FireEye since June 2012.
He previously held executive positions at Oracle, EMC, Documentum, Intel, Segue Software, and Quest Software.
He holds a bachelor's degree in computer science from the University of Delaware
Mr Aziz will become the company's vice chairman and chief strategy officer while retaining the CTO role.