His grandfather Xun Shu, Prefect of Langling, was well known in his day and had eight sons, who were called the Eight Dragons. His father Xun Gun was Chancellor of Jinan, and his uncle Xun Shuang was Minister of Works (sikong). In his youth He Yong of Nanyang called him "a talent to assist a king." In the 1st year of Yonghan (189) he was recommended as Filial and Incorrupt (xiaolian) and became Prefect of the Palace Stores (shougong ling); during Dong Zhuo's upheaval he went out to serve as Prefect of Kangfu, but abandoned his office and returned home. He said that Yingchuan was a land fought over from all four sides and that they should leave at once, but no one followed him, so he alone led his clan to Ji Province. Records, Wei 10 §2–3
By then Yuan Shao had already seized Han Fu's position, and he treated Xun Yu with the courtesy due an honored guest. But Xun Yu judged that Yuan Shao would never accomplish great things, and in the 2nd year of Chuping (191) he followed Cao Cao, then General of Vehement Might (fenwu jiangjun) in Dong Commandery. Cao Cao was overjoyed, called him "my Zifang," and made him his Major; he was twenty-nine at the time. Even after Cao Cao took up the post of Governor of Yan Province, Xun Yu always followed him as Major. Records, Wei 10 §4–5
In the 1st year of Xingping (194), when Cao Cao went to attack Tao Qian, he left Xun Yu in charge of affairs behind him, but Zhang Miao and Chen Gong rebelled with Yan Province and brought in Lü Bu. Realizing that Zhang Miao had risen in revolt, Xun Yu readied his defenses and summoned Xiahou Dun, Administrator of Dong Commandery, who that very night executed several dozen men plotting rebellion. When Guo Gong, Inspector of Yu Province, arrived with a host of several tens of thousands and asked to meet him, Xun Yu went out, saying that Guo Gong had to be persuaded before his plans were settled. Seeing that Xun Yu showed no sign of fear, Guo Gong concluded that Juancheng could not easily be taken and withdrew. Xun Yu also conferred with Cheng Yu and had him win over Fan and Dong'a, so that the three cities were held intact to await Cao Cao. Records, Wei 10 §5–7
In the 2nd year of Xingping (195), when Tao Qian died, Cao Cao wanted to seize Xu Province first. Xun Yu argued that Yan Province was Cao Cao's base, just as Guanzhong had been for Emperor Gaozu of Han and Henei for Emperor Guangwu, and that if he left Lü Bu alone and went east, he would lose Yan Province without gaining Xu Province either. Cao Cao gave up the plan, gathered in a great harvest of wheat, and then fought Lü Bu and pacified Yan Province. Records, Wei 10 §8–12
In the 1st year of Jian'an (196), when Emperor Xian (Liu Xie) returned to Luoyang, some held that Han Xian and Yang Feng, who had the Son of Heaven in their keeping, could not easily be subdued, but Xun Yu cited the examples of Duke Wen of Jin and Emperor Gaozu of Han and urged Cao Cao to receive the Son of Heaven, saying that to uphold the sovereign and follow the people's hopes was the great course in accord with right. When Cao Cao received the Son of Heaven and made Xu the capital, Xun Yu, as Palace Attendant of the Han, acted as Director of the Imperial Secretariat, and even while Cao Cao was campaigning in the field, all military and state affairs were planned together with him. He recommended Xun You, Zhong Yao, Xi Zhicai, Guo Jia, and others, all of whom proved equal to their posts; only Yan Xiang and Wei Kang later came to ruin. Records, Wei 10 §13–16Records, Wei 14 §32
After Yuan Shao had brought the lands north of the Yellow River (Heshuo) under his control and Cao Cao had been defeated by Zhang Xiu at Wan, Yuan Shao sent an arrogant letter. When Cao Cao said that his strength was no match, Xun Yu compared Yuan Shao and Cao Cao on four counts—magnanimity, strategy, military might, and virtue—and said that Cao Cao prevailed on every one. He also said that only after first taking Lü Bu could Cao Cao make designs on Hebei, that Han Sui, Ma Chao, and the others in Guanzhong should be soothed with kindness and brought to terms of peace, and that affairs in the west should be entrusted to Zhong Yao. Records, Wei 10 §17–27
When Kong Rong cited Tian Feng, Xu You, Shen Pei, Feng Ji, Yan Liang, and Wen Chou to argue that Yuan Shao would be hard to defeat, Xun Yu said that if Xu You's family broke the law, Shen Pei and Feng Ji would be unable to overlook it and Xu You would turn against them, and that Yan Liang and Wen Chou had merely the courage of common men. In the 5th year of Jian'an (200), as provisions ran low at Guandu, Cao Cao wrote to discuss returning to Xu. Xun Yu replied that whichever side withdrew first would see its position collapse, and that now was the time to use an unorthodox stratagem. Cao Cao stayed and beheaded Chunyu Qiong and others, and Xu You's defection, the deaths of Yan Liang and Wen Chou, and the execution of Tian Feng all came about just as Xun Yu had reckoned. Records, Wei 10 §29–32
In the 6th year of Jian'an (201), when Cao Cao wanted to attack Liu Biao, Xun Yu dissuaded him, saying that if Yuan Shao gathered his remaining embers and came out behind him, the great enterprise would be lost. In the 8th year of Jian'an (203) he was enfeoffed as Marquis of Wansui Precinct. In the 9th year of Jian'an (204), after the fall of Ye, when Cao Cao was about to follow a proposal to restore the nine provinces of the ancient system, Xun Yu said that the generals west of the passes would be unsettled and that the matter should be discussed only after the realm was fully at peace, and so put a stop to it. Records, Wei 10 §33 · 35–38
Cao Cao married his daughter to Xun Yu's eldest son, Xun Yun. Xun Yu distributed his salary and gifts among his clan and old friends, so that his household had no wealth left over, and in the 12th year of Jian'an (207) his fief reached a total of 2,000 households. When Cao Cao attacked Liu Biao, Xun Yu advised him to march openly toward Wan and Ye while advancing lightly by byways; Liu Biao died of illness, and when Cao Cao advanced according to this plan, Liu Cong surrendered with Jing Province. Records, Wei 10 §40–41
In the 17th year of Jian'an (212), when Dong Zhao and others privately consulted Xun Yu, saying that Cao Cao ought to be raised to the rank of duke and granted the Nine Bestowments, Xun Yu said that Cao Cao had originally raised a loyal army to set the court aright and should keep to loyalty and self-effacement, for a gentleman cherishes others through virtue. Cao Cao was displeased by this. On the campaign against Sun Quan, Cao Cao had Xun Yu reward the troops at Qiao and then kept him there to take part in the military affairs of the Chancellor. When Cao Cao's army reached Ruxu, Xun Yu stayed behind at Shouchun because of illness and died in distress. He was fifty, and was given the posthumous name Marquis Jing. The following year Cao Cao became Duke of Wei. Records, Wei 10 §42–43
His son Xun Yun succeeded to the marquisate. Cao Pi, while contending for the succession, had humbled himself in courtesy to serve Xun Yu, but after Xun Yu's death, when Xun Yun grew close to Cao Zhi, Cao Pi came to hate Xun Yun deeply. Records, Wei 10 §45
In his assessment, Chen Shou said that Xun Yu was pure and outstanding, broadly versed and refined, with the bearing of one who assists a king. Yet he wrote that although Xun Yu had the insight to discern the first signs of things and foresee what was to come, he was unable to fulfill his aims. Records, Wei 10 §90