Jeremy Hunt says he would boost defence spending by £15bn over the next five years if he becomes prime minister.
The Tory leadership candidate’s promise would mean spending on defence would rise to 2.5% of GDP by 2023/24, from its current 2%.
Mr Hunt said the move would “show the world a self-confident country ready to defend its interests and values.”
Defence Secretary Penny Mordaunt, who backs Mr Hunt, said the government must give the armed forces “what they need.”
“Jeremy’s clear commitment to do that is one reason why he has my support,” she added.
Sources close to Mr Hunt suggested the policy would be funded through economic growth and fiscal “headroom” set aside by Chancellor Phillip Hammond.
There has not been a full-scale Strategic Defence and Security Review, looking at future defence challenges and capabilities, since 2015 and one is expected in 2020.