President Donald Trump says Interior Secretary Ryan Zinke – who is facing federal investigations into his travel, political activity and potential conflicts of interest – will leave the administration at the end of the year.
President Trump tweeted that Mr Zinke “accomplished much during his tenure” and that a replacement would be announced next week.
The Cabinet post requires Senate confirmation.
Mr Zinke, a former Republican congressman from Montana, is leaving weeks before Democrats take control of the House, a shift in power that promised to intensify probes into his conduct.
Mr Zinke played a leading part in President Trump’s efforts to roll back environmental regulations and promote domestic energy development.
His departure comes amid a staff shake-up as President Trump heads into his third year in office.