In the immediate prehistorical period, the lowlands of Quảng Trị and central Vietnam as a whole were occupied by Cham peoples (Champa), speaking a Malayo-Polynesian language, and culturally distinct from the Vietnamese to the north along the Red River. The Qin conquered parts of present-day Central Vietnam at the end of the 3rd century BCE, and administered the indigenous peoples of the area through a commandery, Rinan, for several centuries. A rebellion by the Cham in the 2nd century CE overthrew Chinese control and reestablished local government. Beginning in the 14th and 15th centuries, the Chams were defeated in the area by Vietnamese armies, and ethnic Vietnamese gradually displaced or absorbed those Chams who had not fled. Over time a distinct Vietnamese dialectical and cultural subgroup developed in the area. The region was seized by the French by 1874. In 1887 it became part of French Indochina, i.e. the Annam protectorate.
The Quảng Trị Citadel and part of Quảng Trị City looking south, as they were in 1967 Upon the division of Vietnam in 1954 into North and South, Quảng Trị became the northernmost province of the Republic of Vietnam. Beginning 1964, the province gradually became a center for American bases, particularly after October 1966, when the 3rd Marine Division moved to bases just south of the demilitarized zone. In 1966, North Vietnamese forces also began occupying the northern region and pushing deeper into the province.
The provincial capital, Quảng Trị City, was overrun and occupied briefly by Communist troops in April 1967, and was a principle battleground during the 1968 Tet Offensive when it was again overrun by North Vietnamese troops and held for a short period before being recaptured by South Vietnamese government and U.S. forces.
The Battle of Khe Sanh (1968) was a part of the North's steady efforts to occupy the whole of the province. After Khe Sanh was evacuated in July 1968, the North Vietnamese continued their efforts to take the entire province. The most notable achievement of the North Vietnamese offensive in 1972 was capturing Quảng Trị (First Battle of Quảng Trị), although they lost much of the territory gained during the South Vietnamese counter-offensive from June through September 1972 (Second Battle of Quảng Trị).
With South Vietnamese forces unable to hold the province during the final North Vietnamese offensive of the war, the entire province fell to North Vietnamese forces in March 1975. After Quảng Trị fell, the North Vietnamese Provisional Revolutionary Government lay claim to the province. Collective farms were set up and strict rules were enforced on villagers, many of whom eventually fled. According to Gary D. Murfin, who led a survey on Vietnamese refugees after 1975, the province was an area of particularly dense Catholic concentration, most of which was staunchly anti-communist. Murfin estimated that 41% fled the area in fear of Viet Cong reprisals, 37% feared fighting, shelling, and bombing, and others fled because they were a family related to a Nationalist soldier, or were at one point landowners. Today, the province is largely agricultural and rural. The provincial capital of Quảng Trị is Đông Hà.