DeWalt, a 25-year technology industry veteran, will also serve as vice chairman of the board at Optiv, the company said Thursday.
DeWalt previously served as president and CEO of McAfee and spearheaded Intel's $7.7 billion acquisition of McAfee in 2010.
He also held senior leadership roles at EMC, Oracle, Documentum, Segue and Quest Software.
Petraeus is a partner at private equity firm KKR and chairman of the KKR Global Institute.
He is a 37-year Army veteran who previously served as CIA director following his military career.
Optiv CEO Dan Burns said DeWalt's cybersecurity experience and knowledge of the heterogeneous platform delivery model would help the firm support partners and clients as they navigate through the current digital business environment.
Burns added Optiv expects Petraeus to leverage his military and government experience to provide global threat intelligence insights as the company works to help government agencies implement security practices adopted in the private sector.