He hailed from Tianshui 天水 (modern Tianshui, Gansu) and was known for his sincerity and bravery. In 33 BCE he was appointed Protector-general (duhu 都護) of the Western Territories 西域, concurrently commandant of cavalry (jiduwei 騎都尉) and Grand Master of Splendid Happiness (guanglu dafu 光祿大夫).
During his time in the protectorate, no single rebellion occurred. Yet in 31 BCE Qi Man 期滿 stirred up chaos, so that Duan Huizong was transferred as governor (taishou 太守) of the commandery of Peijun 沛郡, later on to Yanmen 雁門.
In 24 BCE, he was allowed to go back to the Western Teritories, where he was finally able to put down Qi Man's rebellion. He was then called to the capital where he served as Leader of the left section of the court gentlemen (zuocao zhonglangjiang 左曹中郎將).