"It is with deep and profound sadness that the family of former Secretary of Defense Ashton B. Carter shares that Secretary Carter passed away Monday evening in Boston after a sudden cardiac event," his family said in a statement.

"He was a beloved husband, father, mentor, and friend. His sudden loss will be felt by all who knew him."

Carter held the top job at the Pentagon from 2015 to 2017 -- a period that covered the height of the war against the Islamic State group, which lost swathes of territory it seized in Iraq and Syria to local ground forces backed by a US-led international coalition.

He also oversaw sweeping changes to the US military, including the opening of combat positions to women and the lifting of a ban on transgender personnel openly serving in the American armed forces.

Former president Donald Trump sought to reverse the latter move, but his administration's restrictions on transgender personnel were overturned by Joe Biden when he took office in 2021.

After leaving the Pentagon, Carter became the director of the Belfer Center for Science and International Affairs at Harvard's Kennedy School.

He is survived by his wife and two children.