The M14 was developed from a long line of experimental weapons based upon the M1 Garand. The M14 was developed as a means of taking the place of four different weapons systems — the M1 Garand, the M1 Carbine, the M3 "Grease Gun" and the M1918 Browning Automatic Rifle (BAR).

 Springfield Armory began tooling a new production line of M14's in 1958 and delivered the first service rifles to the U.S. Army in July 1959. However, long production delays resulted in the 101st Airborne Division being the only unit in the Army fully equipped with the M14 by the end of 1961. The Fleet Marine Force finally completed the change from M1 Garand to M14 in late 1962.

 The M14 rifle served adequately during its brief tour of duty in Vietnam. Though it was unwieldy in the thick brush due to its length and weight, the power of the 7.62 mm NATO cartridge allowed it to penetrate cover quite well and reach out to extended range, developing more than 2,400 ft.lb. of muzzle energy. The weapon also proved to be very reliable and continued to function even under adverse conditions.

 However, there were several drawbacks to the M14. The traditional wood stock of the rifle had a tendency to swell and expand in the heavy moisture of the jungle, adversely affecting accuracy. Fiberglass stocks were produced to resolve this problem, however, the rifle was discontinued before they could be distributed for field use. Also, because of the M14's powerful 7.62 × 51 mm cartridge, the weapon was virtually uncontrollable in fully automatic mode.

 The M14 remained the primary infantry weapon in Vietnam until it was replaced by the M16 in 1966–1968. The M16 was ordered as a replacement for the M14 by direction of Secretary of Defense Robert McNamara, over the objection of Army officers who had backed the M14. Though production of the M14 was officially discontinued, some disgruntled troops still managed to hang on to them while deriding the M16 as a frail and underpowered "Mattel toy" or "poodle shooter".

 The M14 also provides the basis for the M21 and XM25 sniper rifles. The U.S. Army converted several M14s into the M21 sniper rifle, which remained standard issue for this purpose until the adoption of the M24 SWS in 1988.

 M14 variants are still used by various U.S. branches, and in many other armies, especially as a sniper rifle and/or a designated marksman rifle, due to its excellent accuracy and effectiveness at long range.

  Few M14s were in use in the Army until the Afghanistan and Iraq Wars. But since, many M14s are seen in use as designated marksman and sniper rifles. These are not M21 rifle, but modified old M14 or new Springfield Armory, Inc. M21 Tactical Rifles. Several variants exist, ranging from single M14 to highly modified rifles with scopes, fiberglass stocks, etc.