This author and blogger has so far examined the history of Presidents serving as members of the House of Representatives and the US Senate, as State Governors, and as Cabinet Officers.
Now, let’s examine those 8 Presidents who served as US Ambassadors to foreign nations:
John Adams as Ambassador to Great Britain during the Continental Congress
Thomas Jefferson as Ambassador to France during the Continental Congress
James Monroe as Ambassador to France during the George Washington Presidency, and to Great Britain during the Thomas Jefferson Presidency
John Quincy Adams as Ambassador to the Netherlands during the George Washington and John Adams Presidencies; to Germany during the John Adams Presidency; to Russia and to Great Britain during the James Madison Presidency
Martin Van Buren as Ambassador to Great Britain during the Andrew Jackson Presidency
William Henry Harrison as Ambassador to Colombia during the John Quincy Adams Presidency
James Buchanan as Ambassador to Great Britain during the Franklin Pierce Presidency
George H. W. Bush as Ambassador to the United Nations during the Richard Nixon Presidency and as Chief of the US Liaison Office in China during the Gerald Ford Administration.
The most common Ambassadorship was to Great Britain, where five of the eight Presidents listed above served.