Shi Ren was born in Guangyang. According to Yang Xi (楊戯), a former vassal of Shu Han who wrote a historical record for his lord and allies in 241, his name was only Shi Ren. In Guan Yu's scroll in Record of the Three Kingdoms and the Zizhi Tongjian, his name was recorded as Fu Shiren.
He was one of Liu Bei's generals who was stationed in Gong'an County. He went with the Prefect of Nanjun, Mi Fang, to reinforce Jing Province and faced Lu Meng. For reasons not clearly stated, they held a grudge against Guan Yu and worked together to vent their hatred. When Guan Yu sent his army to the war front, both of them refused to send supplies. In response, Guan Yu said, "When we return, we must dispose of Shi Ren and Mi Fang." Both parties remained weary of the other, but neither took any action against the other.
Lu Meng exercised caution, thinking that Shi Ren and Mi Fang would impede his strategies if they were left in their current state. He feigned illness as an excuse to withdraw from the war front. Guan Yu took the bait and went with defenders from Nanjun to pursue their general retreat. Meanwhile, Lu Meng secretly lead troops towards Gong'an Castle, intimidated them with his troops' numbers, and hailed for their surrender with Yu Fan as the messenger. Shi Ren didn't personally see Yu Fan but he responded with a letter depicting his intentions to never aid Wu and his honest desire to only cause harm to Guan Yu. With tears streaming down his cheeks, he surrendered. Lu Meng assigned him to join the march towards Nanjun. Mi Fang saw that Shi Ren was in their army and also submitted.