Tạ Thu Thâu was born in a small hamlet in Tân Bình, 17 km (11 mi) south of Long Xuyên, the capital of An Giang Province in Southern Vietnam. His family were poor and leading a semi-peasant lifestyle. His father was an itinerant village carpenter and when his family was established in Long Xuyên, Tạ Thu Thâu went to primary school, and by working as a servant during holiday periods was able to continue his studies further. He was a brilliant student who went to France for university studies in 1927. Like many of his generation he lived a time when Vietnamese revolutionary nationalism was passing over to Marxism and communism.
Arrested during a protest demonstration against the execution of the Yên Bái rebels in front of the Élysée Palace on 22 May 1930, he was arrested and expelled back to Vietnam. Several left opposition groups were formed - the Communist League in Western Saigon in May 1931, Left Opposition and Indochinese Communism. These groups united and Tạ Thu Thâu was acknowledged as the most notable leader of the Trotskyists in Vietnam. In 1932 the French Colonial authorities arrested many members of the Indochinese Communist Party and the Trotskyists. All left-wing activity in Indochina was clandestine.
However, in 1933 the Saigon Trotskyists and Communists formed an electoral bloc for the elections to the Saigon Municipal Council. The joint 'workers slate' was successful and the Trotskyists Tran Van Thach and Communist Nguyen Van Tao scored the highest votes. Though struck down by the Colonial authorities, this success indicated the growing popularity of the revolutionary groups. The other main activity of the united front was the publication of the legal newspaper La Lutte. The united front split in 1937 over the issue of the 'popular front' policy of the Comintern and under pressure from the Comintern via the French Communist Party.
La Lutte became an openly Trotskyist paper and in 1939, the Trotskyist candidates, Tạ Thu Thâu, Tran Van Thach and Phan Van Hum scored 80% of the vote, defeating three constitutionalists, two Communists and numerous independents. The Indochinese Communist Party vote in this election was one per cent. The Saigon Communists split, and so did the Trotskyists. When the Molotov–Ribbentrop Pact was signed in the summer of 1939, the French authorities declared the Communist Party illegal and in Indochina, all the Communists and the Trotskyists leaders were rounded up. The revolutionary movement was decimated. With more support from farmers, the Communists managed to continue their underground activity in the countryside and began to rebuild. The Trotskyists, reliant on working-class support in the cities, were virtually eliminated as a political force. Tạ Thu Thâu was arrested and incarcerated in Poulo-Condore during the war.
After the end of World War II, Tạ Thu Thâu reconstituted the 'La Lutte' ('The Struggle') group and became the foremost leader of Vietnamese Trotskyism, but in the events of the August Revolution of 1945, and under the impact of the re-establishment of French colonial rule and repression from the Communist-led Viet Minh, his political current lost any significant influence. Tạ Thu Thâu, along with other prominent Trotskyists and nationalists, was assassinated by the Viet Minh in 1945.