George Barnett was born on December 9, 1859, in Lancaster, Wisconsin. He entered the U.S. Naval Academy on June 27, 1877, and graduated with the Class of 1881. After serving the required two years at sea as a Passed Midshipman, Barnett was commissioned a Second Lieutenant in the U.S. Marine Corps on July 1, 1883, and served at Marine Barracks, New York City, from August to October 1883. His next assignment was with Marine Barracks, Mare Island, California, from October 1883 to July 1884, followed by service aboard the screw tug USS Pinta patrolling Alaskan waters from July 1884 to June 1887. He served with U.S. Marine Corps Headquarters in Washington, D.C., from June to August 1887, and then with Marine Barracks, Navy Yard in Washington, D.C., from August 1887 to April 1888. Lt Barnett's next assignment was with Marine Barracks, Newport, Rhode Island, from April to August 1888, followed by service at Marine Barracks, Washington, D.C., from September 1888 to May 1889. He served aboard the sloop of war USS Iroquois as part of the Pacific Squadron from May 1889 to May 1892, and then served with Marine Barracks, Navy Yard in Washington, D.C., from July 1892 to May 1893. Lt Barnett served with the Marine Guard, World's Columbian Exposition, in Chicago, Illinois, from May to December 1893, and then returned to Marine Barracks, Navy Yard in Washington, D.C, where he served from December 1893 to March 1896. His next assignment was with Marine Barracks, Portsmouth, New Hampshire, from March to June 1896, followed by service aboard the store and receiving ship USS Vermont at the Brooklyn Navy Yard from June 1896 to November 1897. He served aboard the protected cruiser USS San Francisco (C-5) from November 1897 to April 1898, and then aboard the protected cruiser USS New Orleans (PG-34) from April to November 1898 as part of the Flying Squadron in combat during the Spanish-American War. Capt Barnett served aboard the protected cruiser USS Chicago from November 1898 to April 1901, and during this time he was promoted to Major in March 1901. His next assignment was with Marine Barracks, Newport, Rhode Island, from July to October 1901, followed by service with the Recruiting District Headquarters at Philadelphia, Pennsylvania, from October 1901 to September 1902. Major Barnett served on the Isthmus of Panama from September to November 1902, and then served as Commander of First Brigade of Marines in the Philippines from January to July 1903. He was transferred briefly to the hospital ship USS Solace (AH-2) in July 1903, and then aboard the battleship USS Kentucky (BB-6) from July 1903 to March 1904. Major Barnett was then transferred briefly to the protected cruiser USS New Orleans (PG-34) in March 1904, followed by service aboard the battleship USS Wisconsin (BB-9) from March to December 1904. His next assignment was as Commander of First Brigade of Marines in the Philippines from December 1904 to April 1905, and during this time he was promoted to Lieutenant Colonel in February 1905. Lt Col Barnett served at the Marine Barracks, Navy Yard, Washington, D.C., from July 1905 to June 1906, and he then attended Naval War College at Newport, Rhode Island, from June to September 1906. His next assignment was as Commander of an Expeditionary Force of Marines in Cuba from September to November 1906 during the 2nd Occupation of Cuba, followed by service with Marine Baracks, Navy Yard, Washington, D.C., from November 1906 to November 1907. He served with Headquarters U.S. Marine Corps in Washington, D.C., from November 1907 to January 1908, and then as Commander of the Marine Detachment, American Legation in Peking, China, from March 1908 to July 1910. His next assignment was to the Marine Barracks, Philadelphia, Pennsylvania, from October 1910 to February 1914, and he was promoted to Colonel at the beginning of this assignment. During this time, Col Barnett served as Commander of the First Regiment, Provisional Brigade of Marines in Cuba from March to June 1911, from May to August 1912, from February to May 1913, and from January to February 1914. He was promoted to Major General and became Commandant of the U.S. Marine Corps on February 25, 1914, and served in this position through the Banana Wars, Mexican Border War, and World War I, from February 1914 to June 1920. After finishing his 6 year term as Commandant of the Marine Corps, Major General Barnett served as the first Commanding General of the Department of the Pacific in San Francisco, California, from November 1920 to August 1923. He retired from the Marine Corps on December 9, 1923, and he died on April 27, 1930. Maj Gen Barnett is buried at Arlington National Cemetery.

His Navy Distinguished Service Medal Citation reads:

The President of the United States of America takes pleasure in presenting the Navy Distinguished Service Medal to Major General George Barnett, United States Marine Corps, for exceptionally meritorious service in a duty of great responsibility as Commandant of the Marine Corps from 25 February 1914 to 30 June 1920, in the administration of his high office and the organization and direction of the manifold and distinguished service of the Marine Corps at home and abroad.