He graduated from Louisiana State University prior to entering into the U.S. Military Academy at Annapolis, graduating in 1888 and completing his two-year cruise in July 1890.
Major General Lejeune was first assigned to the barracks at Norfolk and New York before assuming command of the USS Cincinnati in 1897, which he commanded through the Spanish American War.
In 1899, he assumed command of the Marine Guard aboard the USS Massachusetts until July 1900, when he briefly worked recruiting duty, before reporting to the barracks of Penisola FL. Major General Lejeune was then assigned to the Norfolk Barracks, recruiting duty, D.C. Headquarters, the USS Panther, and finally, the USS Dixie before his assignment in Panama, commanding the marine battalion there.
In 1907 he was transferred to the Philippines, assuming command of the barracks, prison, and yard until 1909, when he returned to D.C.
In 1912, Major General Lejeune, aboard the USS Ohio, toured Guantanamo Bay and the District of Santiago before transferring to the USS Prarie for Panama.
By April 1914, he was in Mexico for the Occupation of Veracruz before returning to D.C.
When WWI erupted, Major General Lejeune was initially assigned to the barracks at Quantico Virginia but was soon transferred to France as the commander of the 4th Brigade of Marine, and then assumed command of the 2nd Division - the first Marine officer to command an Army division. He led his division into Germany.
After the war, he was assigned to the barracks at Quantico until July 1, 1920, when he was named the 13th Major General Commandant of the U.S. Marine Corps, a position he served until March of 1929.
He retired from the U.S. Marine Corps in November 1929 and became the superintendent of the Virginia Military Institute, retiring in 1937.
Major General John A Lejune died on November 20, 1942, and rests in Arlington Cemetary.