In his long career spanning both World Wars, he served as Chief of Mission in eight countries, as Assistant Secretary of State for Political Affairs, and married into Russian nobility.

After the collapse of Czarist Russia, the Bolsheviks seized control of the government and signed the Treaty of Brest-Litovsk with the Central powers, which marked their exit from World War I.

Prior to the formal signing of the treaty, the United States partially evacuated their embassy, but Armour remained as part of the limited staff.

The North Russia Campaign, an Allied Intervention in the Russian Civil War, further destabilized the situation and resulted in the legation becoming essentially under siege.

According to news reports of the time, Armour was arrested and brought back to Moscow, where he and other Americans (diplomats and otherwise) were allowed to flee the country on August 26, by train to Sweden, arriving on September 5.

Contrary to the contemporary reports, his obituary in the New York Times also says that he did not travel in the refugee train from Moscow, but rather escaped himself to Finland, still disguised as a courier, where he caught up with them.

Née Myra Sergueievna Koudashev, Mrs. Armour was a daughter of a first marriage of Tatar Prince Serguey Vladimirovich Kudashev, to a Russian Countess of the Nieroth family, being born in Saint Petersburg, 7 April 1895.

During his time in Canada, the State Department banned marriages between diplomatic personnel and the citizens of foreign countries they served due to potential conflict of interest problems.

Though there were at this time 122 diplomats who had taken foreign wives, Armour's high-profile relationship with his highborn Russian wife and the way in which they were engaged were commonly cited by the press on both sides of the issue.

During this period, Armour worked to negotiate better trade relations with these South American countries, and, once the United States entered the war, to apply pressure on them to not support the Axis powers.

Near the end of the war, on January 26, 1944, Argentina finally caved to pressure from Britain and the United States and broke ties with the Axis powers.

In Spain, Armour continued to apply pressure on the government of Francisco Franco due in part to its support of the Axis powers during the Second World War.