In 1897,[5] he moved west, and joined the staff of the San Francisco Call as a reporter, before enlisting in the United States Army.

[6] As a soldier, he served as a private in the Third Regiment of Artillery, either in Battery K,[7] or Battery L.[8] During his military service, Hart served as a guard on Alcatraz Island during its usage as Alcatraz Citadel, an Army prison,[9] and was seriously injured: while climbing the steps of the lighthouse,[8] possibly to paint the roof,[10] the stairwell gave way under him, dropping him thirty feet into the rocks below,[9] fracturing his leg, which required the amputation of his leg below the knee.

[30] During his time as minister, Albania became a monarchy under Zogu, now King Zog I;[28] President Coolidge recognized the new Albanian government, as one properly created under the constitutional mechanisms of the Albanian Republic;[31] and Zog personally dedicated the new United States Embassy in Tirana,[32] with its large twelve rooms and lavish furnishings,[33] which, with some modifications and renovations, remains the embassy today.

[34] At the time, King Zog was a bachelor, and it was later reported that he reached out to Hart for the diplomat's assistance in finding a wealthy, politically courageous, and beautiful American bride, someone to help him Westernise his country,[35] and that Hart had sent back a list of names, including Natalie Hays Hammond, whom Zog rejected due to lack of wealth.

[40] After some time back in the United States, Hart was nominated by President Herbert Hoover as minister to Iran (then known as Persia) in October 1929.

[51] Though he was successful in persuading the government to allow James Henry Breasted to conduct an archaeological restoration there,[52] most of his tenure involved responses to crises, including the 1930 Salmas earthquake and its aftermath,[53] as well as the kidnapping of American consular officers,[54] by Lurs near Sahneh,[55] in 1932.

[57][9] In 1936, for instance, Hart, backed by the former Secretary of the Treasury, Ogden L. Mills,[59] and joined by Frederick Gardner Clapp, helped negotiate oil rights in Afghanistan for an American firm, at the request of the Afghan and Persian governments.

[60] During World War II, Hart sought to open another front in Albania; his mission was canceled some time before he boarded his flight, the "Yankee Clipper", which would crash on February 22, 1943, leaving fifteen survivors, including Jane Froman.

[61] Hart's health began to fail that year;[16] in late 1946, he stayed at Bethesda Naval Hospital for several months,[9] after a series of operations relating to complications stemming from his Alcatraz injury.