After graduating at the top of his class in 1921, Diệm followed in the footsteps of his eldest brother, Ngô Đình Khôi, joining the civil service in Thừa Thiên as a junior official. Starting from the lowest rank of mandarin, Diệm steadily rose over the next decade. He first served at the royal library in Huế, and within one year was the district chief in both Thừa Thiên and nearby Quảng Trị province, presiding over seventy villages. Diệm was promoted to be a provincial chief (Tuần phủ) in Ninh Thuận at the age of 28, overseeing 300 villages.