Mcmahon, John Eugene was born on December 8, 1860 in Buffalo, New York, United States. Son of Colonel John E. and Esther (Bryan) M.
Bachelor of Arts, Fordham University, 1880. Graduated from the United States Military Academy, 1886, Artillery School, 1898.
Commissioned Second lieutenant 4th Artillery, July 1, 1886. Promoted through grades to major general N.A., December 17, 1917. Instructor modern langs., United States Military Academy, 1890-1891.
Aide-de-camp to Major General A. McD. McCook, 1891-1895. Adjutant general 2d Brigade Provisional Division, 5th Army Corps, June-July, 1898. Adjutant general 2d Brigade, 2d Division, 4th Army Corps, October-November 1898.
Adjutant general United States forces, Puerto Principe, January-May 1899. In Philippines, 1901. President Field Artillery Board, 1907.
Duty General Staff, 1911-1914. Appointed commander 160th Field Artillery Brigade, Camp Custer, Battle Creek, Michigan, September 1917, 5th Division United States of America, December 28, 1917. Home: Utica, New York.