The invention of a military firearm that could produce rapid, repeating fire to overwhelm and repel an attacking force or act as an offensive or defensive force multiplier had been sought for nearly 900 years. Early attempts to invent what today is known as the machine gun did not produce a fully automatic weapon but resulted in often bulky and semi-reliable guns consisting of single shot barrels gathered together and mounted on a gun carriage or tripod. Some of these multi-barreled weapons were hand-held as a pistol or shoulder-arm, and took a considerable time to reload. Though they could be deadly to an attacker, they could be nearly as dangerous to the gunners themselves. Those hand-held arms evolved into repeating arms such as revolvers, semi-automatic pistols and rifles, and fully automatic sub-machine guns and assault rifles. Those arms are not included in this guide.

So-called organ guns or volley guns of various makes and numbers of barrels came into use as early as 1339 during the Medieval-era reign of English King Edward III (1312-1377) and on into the later 19th Century, when they began to be eclipsed by the modern machine gun. They included examples of the medieval Ribaldequin gun also called the "Infernal Machine," the Billinghurst Requa Battery Gun, the Nock Volley Gun, and the Vandenburg Volley Gun.

Not until the mid-1800s was a weapon invented that was practical, for the most part mechanically reliable, and could be reloaded relatively quickly. The best known example was the Gatling Gun. It was the invention of Richard J. Gatling (1818-1903). Other designs made their appearance as well but did not gain the notoriety the Gatling Gun achieved. These other designs included the Montigny Mitrailleuse, the Nordenfelt Gun, the Agar Gun or Union Repeating Gun (also known as the Coffee Mill Gun), and the Gardner Gun.

First invented in 1884 by Hiram Maxim (1840-1916), the modern machine gun came into use in the late 19th Century in such conflicts as the Boer War and the Spanish American War. It saw use in many other places and became notorious for its use by European nations in their pursuit of colonies. The first combat use of the Maxim occurred on October 25, 1893 in modern-day Zimbabwe when 700 police troops of the British South Africa Company's Police (BSAP) were attacked by 3,500 Matabele warriors as British adventurers invaded their kingdom. Five Maxim guns killed about 1,500 warriors. A week later, another battle saw 2,500 warriors killed out of 6,000 due mostly to the Maxim gun's use. Other machine guns including the Colt M1895 "Potato Digger" in 1889, the Hotchkiss 1897 and the Skoda M1893 were produced with varying levels of mechanical reliability, and were much less popular than the Maxim Gun.

The Maxim Gun became the standard and saw exponential growth in demand and nearly universal use in the first decades of the 20th Century. Russian use of Maxims in the defense of Port Arthur during the Russo-Japanese War (1904-1905) caused 6,200 dead among an attacking Japanese infantry force of over 35,000. World War I (1914-1918) saw the use of tens of thousands of Maxim guns of various manufacture. The primary manufacturers were the Vickers, Sons & Maxim Company in Great Britain, the Spandau Company in Germany, Colt-Vickers in the United States, and the Tula Arms Plant in Russia/the Soviet Union. As of 2022, Ukrainian armed forces were using Maxim guns against invading Russian troops.

Other firearms innovators, originating in the United States, including John Moses Browning (1855-1926) produced such famous guns as the M1917 Browning .30 caliber machine gun and an updated version, the M1919. Browning also invented a heavier gun, the M2 .50 caliber machine gun which became known as "Ma Deuce." He also designed a light machine gun for use by soldiers on the move. The Browning Automatic Rifle or BAR. Browning-designed military guns saw service throughout the 20th Century and many serve still well into the 21st Century. Another American, Isaac Newton Lewis (1858-1911) invented the famous Lewis Gun, a light machine gun used on aircraft and by infantry from World War I at least until the end of the Korean War (1950-1953). American Benjamin B. Hotchkiss (1826-1885) who had moved to France in 1867, and was already well-known for his Gatling-type revolving cannons, designed machine guns for the French Army beginning around 1900. Their use continued through World War II (1939-1945).

Innovation and necessity carried the machine gun even further and with a second world war beginning in 1939, new models and improvements to existing guns were widespread. Germany produced the MG-34 and MG-42. Modern versions of the MG-42 are still in use today with many militaries. Hotchkiss machine guns and auto-cannons produced in the United States, France, Japan, Italy and Poland were used by nearly all combatants during World War II and beyond. Other iconic guns of World War II include the British Bren Gun, the American Johnson light machine gun, the German FG-42, and the Soviet Degtyaryov light machine gun (DP series LMGs) and DShK 1938 heavy machine gun. The French FM 24/29 light machine gun replaced the unpopular and unreliable WWI-era Chauchaut light machine gun beginning in 1925.

The technological advances made during World War II and the advent of the Cold War (1947-1991) influenced further machine gun refinements throughout the world. The German MG-42 was the basis for modern-day versions made in Austria, Germany, Italy, Spain, Switzerland and Yugoslavia and influenced the design of such weapons as the American M-60 and the Belgian FN MAG. In the Soviet Union and other Eastern Bloc countries, Russian designs predominated. The best known of these were derivatives and copies of Mikhail Kalashnikov's (1919-2013) AK-47 assault rifle developed into modified versions to serve as light machine guns. The DP series of light machine guns were replaced with Kalashnikov's RPD light machine gun and later the RPK light machine gun. Kalashnikov also invented the PK machine gun. Kalashnikov's designs are still in use with the Russian armed forces and many other nations' armed forces, as well as many paramilitary groups.