In 1913, he became a partner at J.P. Morgan & Co., one of the largest and most powerful commercial and investment banks in the United States during this era, financially backing industrial giants such as General Motors and 3M.

With his proven logistical and intellectual talents, Morrow was sent to France by President Woodrow Wilson to serve as chief civilian aide to General John J. Pershing.

In 1925, Morrow was summoned by his old Amherst College classmate and friend, President Calvin Coolidge,[4] to lead a board of inquiry into aviation in the U.S.

[5] Upon learning the news, the Mexican press had expected that the appointment of a partner of the financial firm J.P. Morgan was "a return to Dollar Diplomacy.

[6] Morrow was widely hailed as a brilliant ambassador, mixing popular appeal with sound economic and financial advice to the Mexican government.

[6] Morrow initiated a series of breakfast meetings with President Plutarco Elías Calles (1924–1928), at which the two would discuss a range of issues, from oil and irrigation to a religious uprising in Mexico.

Morrow's best known accomplishment was his mediation of the conflict between the Mexican government and the Catholic Church in Mexico which had escalated into a violent armed revolt, known as the Cristero rebellion.

[2] It was not in the security interests of the United States for such internal disorder to be occurring in its neighbor to the south, not least because of the flight of Mexican refugees to the U.S. from the regions of conflict.

Portes Gil told a foreign correspondent on May 1 that "the Catholic clergy, when they wish, may renew the exercise of their rites with only one obligation, that they respect the laws of the land.

In 1930 Morrow was elected as a Republican to the United States Senate to fill the vacancy caused by the resignation of Walter Evans Edge.

Following a speaking engagement in New York City, Morrow suffered a stroke in his sleep at his home in Englewood, New Jersey and died the next afternoon on October 5, 1931.

In 1934, Betty Morrow requested that the British diplomat and writer Harold Nicolson write the definitive biography of her late husband.

[16] Nicolson stayed with the family at Englewood and in Maine for several months, drawing on interviews with them, Morrow's partners at J.P. Morgan, and with former Mexican president Plutarco Elias Calles for his book.