A native of Evanston, Illinois, Moseley was an 1899 graduate of the United States Military Academy (West Point).

He was an aide-de-camp to Brigadier General Jesse M. Lee during the Philippine–American War, and later commanded troops during an expedition against the Pulahan on Samar and Leyte.

In 1919, he was appointed to the Harbord Commission, which reviewed relations between the United States and Armenia and provided policy recommendations to the U.S. government.

After retiring, Moseley became a prominent critic of President Franklin D. Roosevelt and the New Deal, and his arguments included strident anti-communism and antisemitism, as well as opposition to immigration and support for fascism and Nazism.

When American Nazi sympathizer George E. Deatherage plotted to launch a coup against Roosevelt in the 1930s, he sought to recruit Moseley as a potential military dictator.

In 1901 Moseley, accompanied by only one other officer, without escort and under conditions of great danger, penetrated a major Philippine insurgent stronghold.

2nd Lt. Moseley and 1st Lt. George Curry convinced Brigadier General Ludovico Arejola to sign the peace agreement in Taban, Minalabac (Philippines) on March 25, 1901.

After commanding the Second Field Artillery Brigade, in 1921 he was detailed as assistant to General Dawes in organizing the newly created Bureau of the Budget.

His actions stopped stray gunfire from Juarez, Mexico, from endangering life and property in adjacent El Paso, Texas, and precluded further incidents.

[4] He served as General Douglas MacArthur's Deputy Chief of Staff during the 1932 Bonus March on Washington, D.C., in the course of which he recorded his fears of a Communist conspiracy against the United States and his identification of Jews with radicals and undesirables.

... Those nations have either passed out of separate existence entirely, or have remained as decadent entities without influence in world affairs.In 1934, Moseley asked MacArthur to consider the immigration issue in terms of military manpower, contrasting a group of "southern lads" of "good Anglo-Saxon stock" with their counterparts from the North with names "difficult to pronounce" that "indicated foreign blood".

In 1936, he proposed that the Civilian Conservation Corps be expanded "to take in every 18-year-old youth in the country for a six-month course in work, education and military training.

He described fascism and Nazism as good "antitoxins" for the United States that would "disappear when the disease of Communism is cured," adding that "the finest type of Americanism can breed under their protection as they neutralize the efforts of the Communists.

"[10] Moseley understood that as a retired general, he remained subject to the War Department's jurisdiction, writing to a friend: "The only good I can do now is in keeping up quite a large correspondence with men who are in a position to influence public affairs.

"[11] Moseley also tried to lobby the New York National Guard adjutant to "cleanse" the state forces of all Jews and persons of color.

[11] When American Nazi sympathizer George E. Deatherage plotted to launch a coup in the 1930s, he sought to recruit Moseley as a potential military dictator.

With Japan absorbed ... with the balance of power so nearly equal in Europe, where is there an ounce of naval or military strength free to threaten us?

"[13] In December 1941, Moseley wrote that Europe's Jews were "receiving their just punishment for the crucifixion of Christ ... whom they are still crucifying at every turn of the road."

[2] Although he had disappeared from the public's view, he continued to influence a generation of other officers, including Albert Wedemeyer, who shared similar beliefs.