He became best known for the decision to allow women to fully serve in the United States military. Carter also removed a ban on transgender people joining the military.
The decisions came after three years of review and an intense debate in the United States.
“It is the right thing to do,” said the then Minister of Defense when the decision was made in December 2015 about the role of women in the military.
After serving as Secretary of Defense, Carter became director of the Belfer Center for Science and International Relations at Harvard University in Cambridge, Massachusetts.
Ash Carter was 68 years old.