It is not known when Ren Huan was born, but it was known that his family was originally from Sanyuan (三原, in modern Xianyang, Shaanxi).
His father Ren Maohong (任茂宏), in order to avoid late-Tang dynasty wars that engulfed the region, fled to Taiyuan, then under the rule of the major warlord Li Keyong the military governor (jiedushi) of Hedong Circuit (河東, headquartered in modern Taiyuan).
Thus, when Li Keyong put him in charge of Zhaoyi Circuit (昭義, headquartered in modern Changzhi, Shanxi), at his request, Ren Huan was made his executive secretary in his role as governor (觀察使, Guanchashi).
He gave his chief of staff Guo Chongtao the post of military governor of Chengde Circuit (成德, headquartered at Zhending), and Ren was made the commander of the Chengde army and the director of supplies in the northern circuits, as well as continuing to serve as the acting mayor of Zhending.
It was said that at Zhang's machinations, the funds that were designated for governmental loans to the people were hidden from the books, purportedly for Ren's benefit.
(Empress Liu had become convinced that Guo was about to rebel, while Li Cunxu, while having his suspicions, refused to believe so, and therefore she decided to issue the order herself.)
[6] Guo's death, and that of another major general, Zhu Youqian, on similarly ungrounded suspicions, caused much unrest in the army ranks and led to a number of mutinies.
[7] After Li Siyuan took the throne, he commissioned Ren Huan and Zheng Jue as chancellors with the designation Tong Zhongshu Menxia Pingzhangshi (同中書門下平章事).
Ren, in addition, was also made the acting director of the three financial agencies (taxation, treasury, and salt and iron monopolies).
It was said that Ren was very conscious of the importance of his duties, and did his best effort to find virtuous and talent people to serve in government and cut off improper ways of advancement.
However, his focus on governance drew jealousy and suspicion from Li Siyuan's powerful chief of staff An Chonghui.
Kong told An that Li Qi was corrupt, and therefore An recommended Cui, leading to further dispute between An and Ren.
[7] Despite the disputes with An, Ren believed that his long-standing relationship with Li Siyuan allowed him to continue to speak boldly, and many other powerful people came to dislike him.
After the imperial meeting was complete, a lady in waiting told Li Siyuan, "When your servant served in the Chang'an palace [(i.e., during Tang)], I did not ever see a chancellor and a chief of staff argue like this.
Ren thereafter requested to resign his acting directorate of the three financial agencies, and Li Siyuan agreed, transferring those authorities to Meng Gu (孟鵠).
An agreed, and persuaded Li Siyuan to issue an order to have Ren commit suicide, despite the protestations of An's associate, the official Zhao Feng.
When the imperial messenger reached Ci, Ren summoned his family members to feast with him, and then committed suicide.