As Administrator of Chen Commandery (陳郡), he was sent to Yangren (陽人) with 5000 men to resist Sun Jian's invasion from the south in 191. Hu Zhen and his comrade Lü Bu, who was in charge of the cavalry, were not on good terms, so Lü Bu spread false rumours confusing the attack. Thus Dong Zhuo's forces under Hu Zhen were heavily defeated by Sun Jian.
After Dong Zhuo's assassination in 192, Hu Zhen served the new government headed by Wang Yun, but he was displeased at Wang Yun's arrogance. When Dong Zhuo's loyalists Li Jue and Guo Si rebelled against the new government, Wang sent Hu Zhen with Yang Ding (楊定) and Xu Rong to fight, or perhaps negotiate, with the rebels. However, Hu Zhen and Yang Ding joined the enemy soon after Xu Rong was killed in battle.
When Li Jue and Guo Si took over the capital Chang'an from Wang Yun, Hu Zhen became the Director of Retainers (司隸校尉) under their command. With his position, he falsely convicted a local officer You Yin (游殷), with whom he quarrelled, and put You Yin to death. A few months later Hu Zhen became ill, saying You Yin's spirit had come for his crime, and died.