Morgenthau was born the ninth of 11 living children, in Mannheim, Baden (present-day Baden-Württemberg, Germany), in 1856 into an Ashkenazi Jewish family.

[6] A few years later, he led a syndicate that bought a swath of undeveloped land in Washington Heights around 181st Street, anticipating the construction of the first subway through the area.

[11] His daughter Ruth married banker and philanthropist George Washington Naumburg[12][13] She was also a civic leader supporting the arts and music.

He substantially reduced the price of the Carnegie Hall sale, [by $500,000] to help Issac Stern's committee and NYC purchase and save the building.

He had first met Wilson in 1911 at a dinner celebrating the fourth anniversary of the founding of the Free Synagogue society and the two "seem to have bonded", marking the "turning point in Morgenthau's political career".

Although he did not gain the chairmanship of Wilson's campaign finance committee, Morgenthau was offered the position of ambassador to the Ottoman Empire.

[27] He initially rejected the position, but following a trip to Europe, and with the encouragement of his pro-Zionist friend Rabbi Stephen Wise, he reconsidered his decision and accepted Wilson's offer.

Although the safety of American citizens in the Ottoman Empire, mostly Christian missionaries and Jews, loomed large early in his ambassadorship, Morgenthau said that he was most preoccupied by the Armenian Question.

[29] After the outbreak of war in 1914, the U.S. remained neutral, so the American Embassy – and by extension Morgenthau – additionally represented many of the Allies' interests in Constantinople, since they had withdrawn their diplomatic missions after the beginning of hostilities.

As Ottoman authorities began the Armenian genocide in 1914–1915, the American consuls residing in different parts of the Empire flooded Morgenthau's desk with reports nearly every hour,[30] documenting the massacres and deportation marches taking place.

[31] The American government however, not wanting to get dragged into disputes, remained a neutral power in the conflict at the time and voiced little official reaction.

Morgenthau held high-level meetings with the leaders of the Ottoman Empire to help alleviate the position of the Armenians, but the Turks waived and ignored his protestations.

Through his friendship with Adolph Ochs, publisher of The New York Times, Morgenthau also ensured that the massacres continued to receive prominent coverage.

"[34] He published his conversations with Ottoman leaders and his account of the Armenian genocide in Ambassador Morgenthau's Story, which appeared in the end of 1918.

In March 1919, as President Woodrow Wilson was leaving for the Conference, Morgenthau was among 31 prominent Jewish Americans to sign an anti-Zionist petition presented by U.S.

The Library of Congress holds some 30,000 documents from his personal papers, including: In Terry George's 2016 drama The Promise, set in the final years of the Ottoman Empire, Morgenthau is played by James Cromwell.