Born in Carlinville, Illinois, he was the grandson and namesake of a famous American Civil War general and Governor of Illinois. He graduated as a 2d lieutenant of infantry in 1892, and served with the 15th US Infantry at Fort Sheridan, Illinois. He participated in the suppression of the Chicago railroad riots of 1894, then went to Cuba as an aide to General Sumner (1898-1899) during the Spanish American War. Following Cuba, he became a member of the China Relief Expedition (1900-1901), then an instructor and assistant professor of chemistry at West Point (1901-1906). Following this academic stint, he was then assigned a billet as a district governor in the Lanao District on Mindanao in the Philippines (1906-1908). Upon return from Far East Service, he was a student at Fort Leavenworth, Kansas and then assigned to the War Department General Staff under the command of the then-Army Chief of Staff Major General Leonard Wood (1908-1910). During this period of service he received recognition as a thinker and writer. In 1910 he rejoined his regiment in Tientsin (Tianjin) China and was promoted to the permanent rank of major. He was then transferred to the 24th Infantry on Corregidor and was instrumental in creating the plans for the defense of the Bataan Peninsula (1914-1916). Following this assignment, he returned to the General Staff in Washington, D.C. (1916) and on the outbreak of the First World War was instrumental in drafting the Draft Act of 1917 and plans for an American Expeditionary Force (AEF). This work caught the notice of General John J. Pershing, who selected Palmer to become his Assistant Chief of Staff, G-3, where he went to France and set up operational plans and staff schools for the American Army. He left the AEF staff due to illness, but recovered in time, as a colonel, to command the 58th Infantry Brigade of the 29th Division in combat against the enemy at Verdun in the Meuse-Argonne Offensive that helped to end World War I.
As the principal formulator of military policy following World War I, he was the guiding force in the creation of the National Defense Act of 1920. It was this Act which reaffirmed America's reliance upon the citizen-soldier for her defense and established the "Total Army" composed of the Regular Army, the National Guard, and the Army Reserve. For his accomplishments, he was made a special advisor to General of the Armies John J. Pershing (1921-1923) and promoted to permanent brigadier general in the Regular Army (1922). He then completed his military career by commanding a brigade in Panama (1924-1926).
In retirement (1926), General Palmer continued to champion the cause of military service. He wrote numerous books and articles about military policy. He was recalled to active duty by Army Chief of Staff George C. Marshall (a personal friend and devotee of Palmer's) just prior to the Pearl Harbor attack and served as an advisor on military policy to the War Department General Staff throughout World War II. He retired quietly soon after the end of the Second World War and lived quietly in Washington, D.C. where he died on October 26, 1955.
A strong advocate of the role of the citizen-soldier in the army of a democracy, Palmer diverged from the views of Emory Upton, with whom he is often compared as a great philosophical thinker-philosopher of the U.S. Army.