"Our force of the future must continue to benefit from the best America has to offer," Carter told reporters. "This includes women."
About 10% of military roles — some 220,000 positions, including those in special operations units and infantry — have only been open to men until now. From January 2016, women will be able to serve alongside men in all of those positions, as long as they meet the same physical requirements.
"This means that as long as they qualify and meet the standards, women will now be able to contribute to our mission in ways they could not before," Carter said. "They'll be able to drive tanks, give orders, lead infantry soldiers into combat."
The Navy and Air Force previously made it clear they were ready for the major transformation within the American military. The Army also condoned the historic shift by permitting women to go through Ranger School.
Based on the results of that study, the Marines requested an exception that would prohibit women from serving in certain areas that may be too physically demanding. But Carter said he "came to a different conclusion," announcing that "there will be no exceptions" to allowing women capable of fulfilling duties from serving in all combat roles, despite potential difficulties with implementing the changes.
"The important factor in making my decision was to have access to every American who could add strength to the joint force," Carter said.