The US Defense Department says Acting Defense Secretary Patrick Shanahan will leave the post by the end of Sunday.
The Pentagon said in a statement that Shanahan and his successor, Army Secretary Mark Esper, met at length on Tuesday to begin transition planning.
The Pentagon said it will work for an orderly transition of authority. It stressed that it will minimize the impact the change may have on US military duties.
Shanahan announced earlier on Tuesday that he was stepping down and that he has asked to be withdrawn from consideration for Secretary of Defense. He cited family reasons.