He became a governor at the age of 81, and was the first person in Korean history to hold such a high-ranking position without taking the civil service exam.

Seo Gyeong-deok and Park Ji-hwa's more academic and ideologically-successful pupils were to join the political faction called Easterners (or Dongin; 동인, 東人) at the Joseon Court.

In 1626, Heo Mok, as the head of management of the dormitory of educational institutions, imposed personal sanctions on scholar Park Ji-gye accusing him of joining King Injo's attempt to destroy the Li.

In 1656, after serving as Jojiseobyuljwa, and as Gongjojwarang (공조좌랑; 工曺佐郞), he was appointed Yonggunghyungam (용궁현감; 龍宮縣監), but resigned shortly after.

In 1659, King Hyojong appointed Heo Mok to Buhogun (부호군; 副護軍), and later that September, he became head of Jangakwon (장악원정; 掌樂院正).

During King Hyojong's funeral, he was in conflict with Song Si-yeol and Song Jun-kil regarding the appropriate length of time for which Queen Jangryeol (자의대비; at the time called "Grand Royal Queen Dowager Jaui"), the second wife of King Injo, should mourn her step-son, based on Confucian rules.

[citation needed] As a result of the dispute, Yeonguijeong Jung Tae-hwa decided to set the mourning period for Grand Royal Queen Dowager Jaui to one year, based on the rules of Gyeongguk daejeon and was the state official solution(which did not differentiate the biological elders and biological second sons), but was considered a political win for Westerners faction.

But Heo Mok and Yun Hyu maintained that Hyojong was the successor of King Injo, which practically made Queen Inseon the first daughter-in-law and required one year of mourning.

In 1675 he was successively appointed for posts such as Yijochampan (이조참판; 吏曺參判), Bibyungukdangsang (비변국당상; 備邊局堂上), Jwachamchan (좌참찬; 左參讚), Yijopanseo (이조판서; 吏曺判書) and Wuchamchan (우참찬; 右參讚).

The Westerners continued to attack Heo Mok and Yun Hyu, calling them Samunanjeok (사문난적; 斯文亂賊).