Fa Zheng, courtesy name Xiaozhi, was a man of Mei County in Fufeng. His grandfather had a name for pure integrity and high repute. When famine struck the realm at the beginning of the Jian'an era, he went to Shu with Meng Da of the same commandery to rely on Liu Zhang, and after serving as Prefect of Xindu he became Colonel of Army Counsel (junyi xiaowei). But he was not given important employment, and, slandered as a man without principles by others who had drifted there from the same region, he could not achieve his ambitions. Zhang Song, Attendant Officer (biejia) of Yi Province, was on good terms with Fa Zheng; judging that Liu Zhang was not worth undertaking great things with, he often sighed in secret. Records, Shu 7 §14
Returning from meeting Cao Cao in Jing Province, Zhang Song urged Liu Zhang to break with Cao Cao and join hands with Liu Bei, and recommended Fa Zheng as envoy. Fa Zheng declined but went because he had no choice. According to Liu Zhang's biography, Liu Zhang then had Fa Zheng and Meng Da lead several thousand troops to help Liu Bei's defenses, and Fa Zheng came back. Fa Zheng praised Liu Bei's great strategic talent to Zhang Song, and the two plotted in secret, hoping to serve Liu Bei together, but had not yet found an opportunity. Records, Shu 7 §15Records, Shu 1 §15
In the 16th year of Jian'an (211), when Liu Zhang grew fearful at news that Cao Cao meant to attack Zhang Lu, Zhang Song persuaded him to invite Liu Bei in to attack Zhang Lu, and Fa Zheng was again sent with the commission. Fa Zheng secretly offered Liu Bei a plan: "Take advantage of Governor Liu's weakness and have Zhang Song respond from within; then, relying on the wealth of Yi Province and the natural defenses of this Land of Abundance, the great enterprise can be achieved as easily as turning over one's hand." Liu Bei met Liu Zhang at Fu County, but when Zhang Song had Fa Zheng propose attacking Liu Zhang there and then, Liu Bei said that it was a great matter and could not be rushed. Records, Shu 7 §15–16Records, Shu 2 §27–29
When Liu Bei went north to Jiameng and then turned south to attack Liu Zhang, Zheng Du advised Liu Zhang to move the people of Baxi and Zitong west of the Fu River, burn all the granaries and the grain in the fields, and hold fast. When Liu Bei, disliking this, asked Fa Zheng about it, Fa Zheng said, "He will never use it, so there is nothing to worry about." Indeed, Liu Zhang dismissed Zheng Du, saying that he had never heard of moving the people to avoid an enemy. Records, Shu 7 §16–18
When the army besieged Luo, Fa Zheng sent Liu Zhang a long letter. He said that Liu Zhang's attendants had sought only pleasing words and made no far-reaching plans, and then pointed out that Zhang Fei's tens of thousands of troops had pacified Badong and entered Qianwei, and that Sun Quan had sent his younger brother, Li Yi, Gan Ning and others to follow, so that Yi Province had lost two parts in three; the General of the Left, he said, had not forgotten old ties, and he urged Liu Zhang to seek a change of course and preserve his house. Records, Shu 7 §18–26
In the 19th year of Jian'an (214), when Chengdu was besieged, Liu Zhang's Administrator of Shu Commandery Xu Jing tried to climb over the wall and surrender but was discovered. After Liu Zhang surrendered, Liu Bei would not employ Xu Jing because of this, but Fa Zheng said that Xu Jing's empty fame had spread throughout the realm, and if he were not treated with courtesy people would say that the lord despised the worthy; he told Liu Bei to follow the example of the King of Yan's treatment of Guo Wei. Fa Zheng became Administrator of Shu Commandery and General Who Displays Martial Might, governing the capital region outside and serving as chief strategist within, and together with Zhuge Liang, Zhang Fei and Guan Yu he was rewarded with five hundred jin of gold and more. Records, Shu 7 §26–27Records, Shu 2 §33Records, Shu 6 §18
Fa Zheng repaid every kindness, even a single meal, and every grudge, even a sidelong glare, and on his own authority killed several men who had slandered him. When someone told Zhuge Liang to curb his power, Zhuge Liang replied that when their lord was at Gong'an, fearing Cao Cao to the north and Sun Quan to the east and, close at hand, dreading trouble from Lady Sun, Fa Zheng had served as his wings, so he could not be stopped. Chen Shou added that Zhuge Liang spoke this way because he knew how much Liu Bei cherished and trusted Fa Zheng. Records, Shu 7 §28–29
After Liu Bei pacified Yi Province and Lady Sun returned to Wu, his ministers urged him to take as his wife the sister of Wu Yi, who had been widowed after marrying Liu Yan's son Liu Mao. When Liu Bei hesitated because he was of the same clan as Liu Mao, Fa Zheng said, "In terms of closeness of kinship, how can it compare with that between Duke Wen of Jin and Ziyu?" and Liu Bei took her as his wife. Fa Zheng also drew up the Shu Code, the laws of Shu, together with Zhuge Liang, Liu Ba, Li Yan and Yi Ji. Records, Shu 4 §9–10Records, Shu 8 §33
In the 22nd year of Jian'an (217), Fa Zheng said that Cao Cao, having made Zhang Lu surrender, had gone back north leaving only Xiahou Yuan and Zhang He because of troubles at home, so if they attacked with their full force they would surely win. If they won, he said, at best they could overthrow the enemy, next they could nibble away at Yong and Liang provinces, and at the least they could hold the strategic points and endure for a long time. Liu Bei approved and advanced on Hanzhong, and Fa Zheng went with him. Records, Shu 7 §30–31
In the 24th year of Jian'an (219), Liu Bei crossed the Mian River southward from Yangping and set up camps at Mount Dingjun and Xingshi. When Xiahou Yuan came to contest the ground, Fa Zheng said, "Now we can strike," and Liu Bei had Huang Zhong attack from the heights with drums beating and battle cries, crushing Xiahou Yuan's army and beheading Xiahou Yuan and others. On hearing that this had been Fa Zheng's plan, Cao Cao said, "I knew Xuande could not have done this; he must have been taught by someone." Records, Shu 7 §31–32
When Liu Bei became King of Hanzhong, Fa Zheng became Director of the Imperial Secretariat and General Who Protects the Army (hujun jiangjun). He died the following year, the 25th year of Jian'an (220), at the age of forty-five; Liu Bei wept for him for several days, gave him the posthumous title Marquis Yi, and granted his son Fa Miao the rank of Marquis Within the Passes. Zhao Yun's biography records that Fa Zheng was the only one to receive a posthumous title in the First Sovereign's time. Zhuge Liang differed from Fa Zheng in his tastes but they respected each other for the sake of the public good, and he always marveled at Fa Zheng's resourcefulness. In the 2nd year of Zhangwu (222), when the great army that attacked Sun Quan was badly defeated and halted at Baidi, Zhuge Liang sighed, "Had Fa Xiaozhi been alive, he could have restrained our sovereign and kept him from going east." Records, Shu 7 §31 · 33–34Records, Shu 2 §40Records, Shu 6 §41
In his assessment, Chen Shou said that Fa Zheng clearly foresaw success and failure and had extraordinary plans and stratagems, but was not praised for virtue and integrity, and wrote that, compared with the ministers of Wei, Pang Tong was next after Xun Yu and Fa Zheng was a match for Cheng Yu and Guo Jia. Records, Shu 7 §36