The company said Friday that its board of directors asked for and received the resignation of Christopher Kubasik from his role as vice chairman, president and chief operating officer.
The 51-year old was previously scheduled to become CEO in January.
Lockheed Martin says an ethics investigation confirmed that he had a close personal relationship with a subordinate employee. That violates the company's code of ethics and business conduct.
The board elected the executive vice-president of its electronics systems business to take his role. Marillyn A. Hewson will serve as president, chief operating officer and director immediately and take over as CEO in January.