The French colonial empire was heavily involved in Vietnam in the 19th century; often French intervention was undertaken in order to protect the work of the Paris Foreign Missions Society in the country. To expand French influence in Asia, Napoleon III of France ordered Charles Rigault de Genouilly with 14 French gunships to attack the port of Đà Nẵng (Tourane) in 1858. The attack caused significant damage, yet failed to gain any foothold, in the process being afflicted by the humidity and tropical diseases. De Genouilly decided to sail south and captured the poorly defended city of Gia Định (present-day Ho Chi Minh City). From 1859 during the Siege of Saigon to 1867, French troops expanded their control over all six provinces on the Mekong delta and formed a colony known as Cochinchina.

A few years later, French troops landed in northern Vietnam (which they called Tonkin) and captured Hà Nội twice in 1873 and 1882. The French managed to keep their grip on Tonkin although, twice, their top commanders Francis Garnier and Henri Rivière, were ambushed and killed fighting pirates of the Black Flag Army hired by the mandarins. The Nguyễn dynasty surrendered to France via the Treaty of Huế (1883), marking the colonial era (1883–1954) in the history of Vietnam. France assumed control over the whole of Vietnam after the Tonkin Campaign (1883–1886). French Indochina was formed in October 1887 from Annam (Trung Kỳ, central Vietnam), Tonkin (Bắc Kỳ, northern Vietnam) and Cochinchina (Nam Kỳ, southern Vietnam), with Cambodia and Laos added in 1893. Within French Indochina, Cochinchina had the status of a colony, Annam was nominally a protectorate where the Nguyễn dynasty still ruled, and Tonkin had a French governor with local governments run by Vietnamese officials.