承天順化省
Ngoãn was born on 4 November 1930 in Phong Bình Commune, Phong Điền District, Thừa Thiên–Huế Province. He was descended from a poor intelligentsia family. His father was a teacher, and his mother was a farmer. Thanh Hải attended local schools through his childhood. When Thanh Hải was 17, he took part in revolutionary movements at Hương Thủy District, and became the commissar of a cultural and artistic troupe. During the 1954-1964 period, Thanh Hải took part in revolutionary movements in his native province, became a provincial propaganda and instruction cadre.