After the Geneva Accords and French withdrawal from Vietnam in 1954, Thụ enrolled in the Tô Ngọc Vân Fine Art course in 1955. In 1957, Thụ was one of 15 students in the first course of the Vietnam Fine Arts College and graduated in 1962. It was here that he first began to experiment with silk painting and woodcarving, techniques that he maintained and mastered throughout his artistic career. At the same time as enrolling into the diploma course of the Vietnam Fine Arts College, Thụ also became one of the founding members of the Vietnam Fine Arts Association. After graduating, he was retained as a school lecturer in the Painting Faculty due to his excellent academic performance.
“In my childhood and adulthood, I lived for many years in the mountainous areas of Việt Bắc and the Northwest. The poetic image of the mountains and forests with simple, rustic people full of emotion is very simple with the silk material that I love.”
Nguyễn Thụ 
Like many painters of his generation who grew up and actively participated in the resistance movement, Thụ was drawn to Hồ Chí Minh as a subject. Many of Thụ’s paintings concentrated on the everyday life of the Democratic Republic of Vietnam’s (DRV) influential leader, portraying him as a kind, generous, calm and welcoming father-figure to all North Vietnamese.
As a lecturer during the escalating Second Indochina
“Painter Nguyễn Thụ is particularly heavy with Tay, Thai and northern mountainous people. People and scenery of the mountain region become a topic throughout the compositions of this talented painter, with lyrical beauty, imbued with mountains and forests, full of poetic and flexible.”
Researcher and painter Phan Cẩm Thượng 
On his travels through the districts of Chỉ Lặng, Bắc Sơn, Hữu Lũng, Tràng Định and the towns of Lạng Sơn and Đồng Dạng, Thụ captured the tradition of anti-French resistance against the mountain landscape. On his travels south of Hanoi, Thụ created a Quảng Bình militia series, documenting their struggle towards reunification.
After painter Nguyễn Phan Chánh, Thụ was largely considered one of the few Vietnamese painters who specialized in painting on silk. However, during the Second Indochina War, Thụ used an array of improvised materials to sketch and paint, including medicines, pastels and grape juice.
In late 1970 and early 1971, Thụ was selected to represent Vietnam in an international exhibition in Eastern European Soviet states alongside the painter Quang Thọ. The exhibition highlighted North Vietnam’s anti-American resistance in Hungry, Bulgaria and Albania. Thụ also had the opportunity to create a landscape painting of the Revolutionary Museum in Moscow.
In 1977, Thụ was made deputy principal of the Vietnam Fine Arts College and later promoted to principal of the college from 1985 to 1991, succeeding Victor Tardieu, Esvariste Jonchere, Tô Ngọc Vân, Trần Văn Cẩn and Trần Đình Thọ. In 1978 he was elected to the Executive Board of the Vietnam Fine Arts Association.