Lê Trọng Tấn participated in the Viet Minh movement before the August Revolution in 1945 and gradually became one of the most important figures of the Vietnam People's Army during the Second Indochina War.

Lê Trọng Tấn was widely appreciated by his comrades, whom of which include general Võ Nguyên Giáp, as one of the finest commanders of the Vietnam People's Army.

From 1954 to 1960, Lê Trọng Tấn was appointed Director of the Vietnam Academy for Infantry Officers and Deputy Chief of the General Staff (Phó Tổng tham mưu trưởng) from March 1961 to 1962.

It was the 4th Company of 1st Regiment, 2nd Corps under his command that arrived first at the Independence Palace, the workplace of the President of the South Vietnam, and arrested the president Duong Van Minh[6] coincidentally it was also a unit of the 312th Brigade commanding by Lê Trọng Tấn which was first came to the French headquarters and captured general Christian de Castries marking the end of the Battle of Dien Bien Phu.

[7][8][9] After the war, Lê Trọng Tấn continued to hold the position of Deputy Chief of the General Staff and Director of the Advanced Military Academy (Học viện Quân sự cấp cao).