"It's purely a personal issue," Harward told The Associated Press on Thursday evening. "I'm in a unique position finally, after being in the military for 40 years to enjoy some personal time."
Trump is searching for a replacement for Army Lt. Gen. Michael Flynn, who resigned on Monday over phone calls with the Russian ambassador to the United States. The discussions of the phone call delved into sanctions leveled against the country during the Obama administration.
Harward is a former Navy Seal, who has spent over 40 years in the Navy and was in President Bush's National Security Council. He has experience in many Middle Eastern countries, including Bosnia and Somalia.
Harward left the military in a position with Lockheed Martin based in the UAE as chief executive for defense, responsible for strategy, operations and growth. He had been considered a front runner for the job which is currently being held by Army Gen. Keith Kellogg in an acting capacity.
On Thursday, Trump said he did not believe Michael Flynn did anything wrong, but said he did not direct Flynn to call the ambassador and discuss sanctions.
"I fired him because of what he said to Mike Pence, very simple," Trump said.
In announcing his resignation on Monday, Flynn said he briefed the President- Elect with incomplete information.