Orphaned young, he lived at the post of his grand-uncle Lu Kang, Administrator of Lujiang; when Yuan Shu was about to attack Lu Kang, he returned to Wu with his relatives, and, being older than Lu Kang's son Lu Ji, he took charge of the family's affairs. When Sun Quan became a general, Lu Xun, then twenty-one, entered his headquarters, and as Commandant of Agricultural Garrisons (tuntian duwei) at Haichang, also in charge of the county's affairs, he gave relief to the drought-stricken people. With troops he had gathered under his own command he subdued the remote and rugged areas until his personal following numbered over two thousand, and after attacking You Tu, a bandit leader of Poyang, he became Colonel Who Establishes Might (dingwei xiaowei). Records, Wu 13 §2–4
Sun Quan gave him the daughter of his elder brother Sun Ce in marriage. When Lu Xun proposed attacking the mountain bandits and picking out the best of them as troops, arguing that distant aims were hard to pursue while the interior remained unsettled, Sun Quan made him Right Division Commander of the headquarters guard (zhangxia you budu). When Fei Zhan, a bandit leader of Danyang, accepted seals from Cao Cao and stirred up the Shanyue, Lu Xun, with only a few troops, set out banners, drums, and horns all around, slipped into the mountain valleys at night, and advanced beating the drums, scattering the enemy. He organized the people of the three eastern commanderies into units and obtained tens of thousands of crack troops. Lu Xun even praised Chunyu Shi, Administrator of Kuaiji, who had lodged accusations against him, as a good official, and Sun Quan said this was the conduct of a true man of virtue. Records, Wu 13 §5–7
When Lü Meng pleaded illness and came to Jianye, Lu Xun went to see him and said that Guan Yu, proud of his valor and overbearing toward others, was bent solely on advancing north, and that if he heard the general was ill he would be all the more off his guard. When Sun Quan asked who could take Lü Meng's place, Lü Meng recommended Lu Xun, saying he was a deep thinker capable of bearing a heavy burden, and that, not yet widely known, he would not be someone Guan Yu feared. Sun Quan made Lu Xun Lieutenant General (pian jiangjun) and Right Division Commander to replace Lü Meng. Records, Wu 13 §7–9
Arriving at Lukou, Lu Xun sent Guan Yu a letter extolling him: even Duke Wen of Jin's campaign at Chengpu or the Marquis of Huaiyin's stratagem in taking Zhao, he wrote, could not surpass the feat of capturing Yu Jin and the others; and he belittled himself as a careless, slow-witted scholar. Guan Yu was greatly reassured and harbored no further suspicion. Sun Quan secretly sent his troops upriver with Lu Xun and Lü Meng in the van, and on arrival they took Gong'an and Nan Commandery at once; Lu Xun, concurrently Administrator of Yidu, became General Who Pacifies the Borders and Marquis of Huating. This was in the 11th month of the 24th year of Jian'an (219). He went on to defeat the generals of Shu, and those he killed, captured, or won over numbered in the tens of thousands in all; as Protector of the Army of the Right and General Who Guards the West, he was promoted in fief to Marquis of Lou. Records, Wu 13 §9–15
When Liu Bei led a great army toward the western border, Sun Quan made Lu Xun Grand Commander with the tally of authority, commanding 50,000 men including Zhu Ran, Pan Zhang, Song Qian, Han Dang, Xu Sheng, Xianyu Dan, and Sun Huan, to resist him. Liu Bei set up dozens of camps in a continuous line from Wu Gorge and Jianping to the borders of Yiling. When Wu Ban pitched camp on level ground to provoke a battle, the generals wanted to attack, but Lu Xun, saying there must be a trick, had them wait and watch, and Liu Bei did indeed emerge from a valley leading 8,000 men who had lain in ambush. When the generals said he should have been attacked at the outset, Lu Xun replied that he had stayed so long that his troops were weary and his spirit broken, and that now was precisely the time to strike. Records, Wu 13 §17–20
His first attack on a single camp failed, so Lu Xun had each soldier carry a bundle of thatch grass and attacked with fire. He beheaded Zhang Nan, Feng Xi, the barbarian king Shamoke, and others, and destroyed more than forty camps; Liu Bei climbed Ma'an Mountain, but his army collapsed, and under cover of night he barely made it into Baidi. Liu Bei said, "That I should be broken and humiliated by Lu Xun—how could this not be the will of Heaven!" The biography of the Sovereign of Wu records that the fighting lasted from the first month of the 1st year of Huangwu (222) until the intercalary month, and the biography of the First Sovereign, calling him by his original name Lu Yi, records that he crushed the First Sovereign's army at Xiaoting. Records, Wu 13 §21–22Records, Wu 2 §41Records, Shu 2 §71
In this campaign, generals who were veterans from Sun Ce's time or noble kinsmen of the ruling house would not obey orders, so Lu Xun, with his hand on his sword, told them that although he was a scholar, he had received his lord's command because he could endure humiliation and bear a heavy burden, and that they must not disobey military orders. Only when they saw that most of the plans had come from Lu Xun did the generals submit. When Sun Quan asked why he had not reported this, he answered that he had admired the principle by which Lin Xiangru and Kou Xun deferred to others; Sun Quan made him General Who Supports the State and Governor of Jing Province, and changed his fief to Marquis of Jiangling. When requests to attack Liu Bei at Baidi again followed one after another, Lu Xun, together with Zhu Ran and Luo Tong, said they should return because Cao Pi was massing troops, and the Wei army did indeed take the field. Records, Wu 13 §24–28
After Liu Bei died and Zhuge Liang made peace with Sun Quan, Sun Quan had his own seal carved and kept with Lu Xun, and first showed him the letters he sent to Liu Shan and Zhuge Liang so that he could revise them. In the 7th year of Huangwu (228), when Zhou Fang, Administrator of Poyang, lured Wei's Grand Marshal Cao Xiu in with a ruse, Lu Xun was granted the yellow axe and made Grand Commander; taking the central division himself, with Zhu Huan and Quan Cong as his left and right wings, he broke Cao Xiu's ambush and pursued him as far as Jiashi. Those killed or captured numbered over ten thousand, and Sun Quan had Lu Xun covered with his own imperial canopy as he passed in and out of the palace gates. Records, Wu 13 §28–31
In the 1st year of Huanglong (229) he became Senior General-in-Chief (shang da jiangjun) and Right Protector-General, assisting the crown prince at Wuchang and managing the affairs of Jing Province and the three commanderies including Yuzhang. When Sun Quan wanted to attack Yizhou and Zhuya, Lu Xun remonstrated that there was nothing to gain, but Sun Quan attacked Yizhou, and what he gained did not make up for what he lost. When Gongsun Yuan broke his alliance and Sun Quan wanted to cross the sea to attack him in person, Lu Xun remonstrated that he should not abandon the foundation of Jiangdong over a small grievance, and his advice was accepted. Records, Wu 13 §32 · 36–42
In the 5th year of Jiahe (236), when he attacked Xiangyang together with Zhuge Jin, Han Bian, who had carried a memorial to the throne and was on his way back, was captured by the enemy. When Zhuge Jin urged a hasty departure, Lu Xun had his men hurry to plant turnips and beans, and played go and archery games with his generals. Saying that if they withdrew at once, the enemy would think them afraid and give chase, he put Zhuge Jin in charge of the boats while he himself led the troops and horses toward the city of Xiangyang, and the enemy hastily returned to the city. Lu Xun calmly put his units in order and withdrew to the boats, and on the way back he attacked Shiyang and other places, killing or capturing over a thousand people. Records, Wu 13 §43–46
In the 7th year of Chiwu (244) he succeeded Gu Yong as Chancellor. When the two palaces of the crown prince and the Prince of Lu came into conflict, Lu Xun submitted three or four memorials saying that the crown prince was the rightful heir and must be as firm as a rock, and asked to go to the capital to speak in person, but was not permitted. His nephews Gu Tan, Gu Cheng, and Yao Xin were exiled for having sided with the crown prince, and Wu Can, Grand Tutor to the Crown Prince, died in prison for having exchanged letters with Lu Xun. When Sun Quan repeatedly sent palace envoys to reproach him, Lu Xun died in anger and grief at the age of sixty-three, leaving no wealth in his household. This was in the 2nd month of the 8th year of Chiwu (245). His second son Lu Kang succeeded him, and in the time of Sun Xiu he was posthumously named Marquis Zhao. Records, Wu 13 §52 · 54–56 · 58Records, Wu 2 §103
In his assessment, Chen Shou said that Liu Bei was acclaimed as a hero throughout the realm and feared by his whole generation, yet Lu Xun, in the prime of life and before his authority and fame were established, overcame and defeated him. Marveling at Lu Xun's strategy and admiring Sun Quan's eye for talent, he wrote that Lu Xun, loyal and utterly sincere, lost his life through his concern for the state, and so could very nearly be called a minister of the altars of the state. Records, Wu 13 §91