When the Yellow Turbans rose in rebellion against the Han, Yu Jin served under Bao Xin who was recruiting soldiers in Juping county. However, he would later come to serve Cao Cao, who was gathering an army to combat Dong Zhuo. Yu Jin was installed as a subordinate of the respecting Wang Lang, and Wang Lang recommended for him to become a general. After meeting and having a discussion with Yu Jin, Cao Cao promoted him to the position of a commander.
In 206 AD, Chang Xi, who was both a friend of Yu Jin's and a constant rebel towards Cao Cao, rose up in opposition once again. Yu Jin was able to get Chang Xi to surrender. The other generals wanted to send Chang Xi to Cao Cao for further action, but Yu Jin knew the military code and despite the friendship, had Chang Xi executed. He wept at the man's funeral, and Cao Cao began to fully utilize Yu Jin, promoting him to General of Tiger's Might after he pacified Tonghai. Zhang Liao was able to prevail against the rebelling Chen Lan and Mei Cheng with Yu Jin's aid.
Yu Jin was sent to assist Cao Ren in warding off a general of Liu Bei, Guan Yu, from Fan Castle. The season permitted heavy rain, and the land was flooded. Yu Jin and his soldiers took onto a higher ground, but Guan Yu attacked them with his army on a large boat. The men of Cao were captured, and Yu Jin surrendered, while a fellow officer, Pang De, refused to surrender and was executed. Cao Cao, upon hearing the events, lamented how Yu Jin had been an actively loyal general for more than two decades, yet he failed to honor the duty of dying for one's lord, unlike Pang De.
When the forces of Sun Quan surprised and captured Guan Yu, Yu Jin was released.
The heir of Cao Cao, Cao Pi, usurped the emperor and started the Wei dynasty. Yu Jin, whose hair was graying, was summoned to an audience with Cao Pi, and Yu Jin collapsed and wept upon seeing him. Cao Pi comforted Yu Jin and ordered him to be sent off as an emissary to Sun Quan, but before doing so had to honor Cao Cao at his mausoleum in Ye. Cao Pi had had men paint murals beforehand, and the murals depicted the battle of Fan Castle with Pang De angered at Guan Yu's victory, and Yu Jin surrendering. After seeing the mural, Yu Jin became sick and died.
Yu Jin was known for his extremely strict adherence to military law. He also shared his spoils from the enemy with his men, and many generals, including Cao Cao held him in great respect. However, it has been observed that Yu Jin could not win his soldiers' hearts to the fullest extent.