Ben Wallace says he will step down as defence secretary at the next cabinet reshuffle after four years in the job.
He told the Sunday Times he would not stand at the next general election, but ruled out leaving “prematurely” and triggering a by-election.
Mr Wallace has served as defence secretary under three prime ministers and has played a high-profile role in the UK’s response to the Ukraine war.
Sources told the BBC they expect the next reshuffle in September.
Rishi Sunak is reportedly planning to shake up his top team, but no date has been confirmed.
Mr Wallace said he was quitting frontline politics due to the toll it had taken on his family, and allies of his have said the decision was not a reflection on Mr Sunak’s leadership.
His Wyre and Preston North constituency is set to disappear at the next election under upcoming boundary changes and he told the newspaper he would not seek a new one.
The 53-year-old’s confirmation of his plans to the Sunday Times comes after days of speculation that he was considering leaving government.
He has always been popular with Tory party members and his decision is likely to be seen as quite a blow for the party by some Conservatives.
It also leaves a big vacancy in government, which Rishi Sunak will have to fill.