As a youth he crossed the Yangtze southward and relied on his sister's husband Deng Dang. Deng Dang was a commander under Sun Ce, and at fifteen or sixteen Lü Meng secretly followed him to attack the enemy; to his angry mother he said, 'If you do not search the tiger's den, how can you get the tiger's cub?' Later he killed with his sword an official who had mocked and insulted him and fled, then gave himself up; Sun Ce summoned him, found him remarkable and kept him at his side. When Deng Dang died, on Zhang Zhao's recommendation he replaced him as Major of a Separate Command. Records, Wu 9 §56–57
After Sun Quan took charge of affairs and planned to merge the units of commanders with few troops, Lü Meng bought crimson uniforms and leggings for his men on credit and drilled them, and instead received more troops. He distinguished himself in the campaign against Danyang and became Commandant Who Pacifies the North. When Huang Zu was attacked in the 13th year of Jian'an (208), he led the vanguard and personally cut off the head of Huang Zu's Area Commander Chen Jiu, and was made General of the Household Who Sweeps the Plains. Records, Wu 9 §58–59Records, Wu 2 §11
That year, together with Zhou Yu and Cheng Pu, he defeated Lord Cao at Wulin and besieged Cao Ren at Nan Commandery. When Gan Ning at Yiling was surrounded by Cao Ren, Lü Meng vouched that Ling Tong could hold out for ten days and proposed that they go to the rescue together, and urged Zhou Yu to send 300 men to block the steep road with felled trees. At Yiling they killed more than half of the enemy, and from the enemy who abandoned their horses and fled they captured 300 horses. When Cao Ren withdrew and they took Nan Commandery, he became Lieutenant General. Records, Wu 9 §60–62
On his way to Lukou to replace Zhou Yu, Lu Su called on Lü Meng. Lü Meng warned Lu Su, who would now be Guan Yu's neighbor, that Guan Yu was a man like a bear or a tiger and laid out five plans for him; Lu Su patted his back and said, 'I did not know your talent and strategy had reached this point,' then paid his respects to Lü Meng's mother and bound himself to him in friendship. When Sun Quan wished to attach the troops of three commanders who had died to Lü Meng, he declined, saying that although their sons and brothers were young, their units should not be abolished. Records, Wu 9 §63–65
When resisting Lord Cao at Ruxu, he advised building a fort flanking the mouth of the river, and Lord Cao could not take it and withdrew. When Zhu Guang, whom Lord Cao had sent as Administrator of Lujiang, opened up extensive rice fields at Wan, Lü Meng advised that he be eliminated early. In the 19th year of Jian'an (214), when Wan was attacked, he recommended Gan Ning as Commander of the Wall-Scaling Troops and beat the drum with his own hands, and the city fell by about breakfast time. Zhu Guang was captured, and Lü Meng became Administrator of Lujiang. Records, Wu 9 §66–68Records, Wu 2 §19
In the 20th year of Jian'an (215) Sun Quan sent Lü Meng to seize the three commanderies of Changsha, Lingling and Guiyang. While Hao Pu, Administrator of Lingling, held out, Liu Bei sent Guan Yu, and Sun Quan wrote to Lü Meng to come back and help Lu Su. Lü Meng concealed the letter and had Deng Xuanzhi, an old friend of Hao Pu, tell him that the General of the Left was surrounded by Xiahou Yuan in Hanzhong and no relief would come. When Hao Pu, afraid, came out of the city, Lü Meng showed him the letter, clapped his hands and laughed, and Hao Pu was so ashamed that he wished to sink into the ground. Later, when Liu Bei asked for an alliance, Sun Quan returned Lingling. Records, Shu 2 §35Records, Wu 9 §69–75
When the army was withdrawing from Hefei and was attacked by Zhang Liao, he and Ling Tong fought to the death to protect Sun Quan. When Lord Cao again came out to Ruxu, Lü Meng, as commander, placed 10,000 strong crossbows on the fort and broke Lord Cao's vanguard before it had finished setting up camp. He became Left Protector of the Army and General of Tiger Might. When Lu Su died in the 22nd year of Jian'an (217), he was stationed at Lukou and took over Lu Su's troops. Records, Wu 9 §76–77 · 53
Lü Meng judged that Guan Yu had a mind to swallow up others and that, being upstream of the state, his position could not last long, and he secretly advised that Guan Yu should be dealt with while Wu was still strong. When Sun Quan asked about attacking Xu Province, he replied that even if Xu Province were taken, Cao Cao would soon come to contest it, and that it would be better to attack Guan Yu and hold the whole of the Yangtze. At Lukou he outwardly redoubled his kindness and kept on good terms with Guan Yu. Records, Wu 9 §77–80
When Guan Yu, attacking Fancheng, left garrisons at Gong'an and Nan Commandery, Lü Meng memorialized that if he returned to Jianye on the pretext of treating his illness, Guan Yu would withdraw the garrisons, and they could then strike the undefended places. He then claimed to be gravely ill, and Sun Quan openly recalled him while secretly making plans with him. Asked who should replace him, he recommended Lu Xun, who was not yet well known and whom Guan Yu would not be wary of. Guan Yu did indeed gradually send his garrison troops to Fancheng. Records, Wu 9 §81–82Records, Wu 13 §9
At Xunyang, Lü Meng hid his elite troops inside covered boats, had men in white clothes row, and, disguised as merchants, pressed on day and night; he captured all the lookouts along the river so that Guan Yu learned nothing. When he reached Nan Commandery, Shi Ren and Mi Fang surrendered. Lü Meng comforted the families of Guan Yu and his officers and men, and with tears beheaded a man from his home region who had taken a single bamboo hat from a commoner's house to cover government armor. He treated Guan Yu's messengers generously and let them know that the families were safe, so that Guan Yu's troops lost the will to fight; Guan Yu fled to Maicheng and was captured when Zhu Ran and Pan Zhang cut off his path. Records, Wu 9 §82–85
He became Administrator of Nan Commandery and was enfeoffed as Marquis of Chanling, but before the enfeoffment was conferred his illness flared up. Sun Quan kept him in the inner hall at Gong'an and bored a hole in the wall to watch whether he could swallow his food. Lü Meng died in the inner hall at the age of forty-two; he had deposited the gold, treasures and gifts he had received in the government storehouse, instructed that they all be returned on the day he died, and asked for a simple funeral. The Records do not give the year of his death. When his illness was grave he recommended Zhu Ran as his successor. Later, discussing men with Lu Xun, Sun Quan said that once Ziming had grown up his learning had increased and his strategies were extraordinary, ranking next to Gongjin, and that in his plan to take Guan Yu he surpassed Zijing. Records, Wu 9 §86–87 · 90 · 92Records, Wu 11 §15
In his assessment, Chen Shou said that Lü Meng was brave and also resourceful and decisive in military planning, and that his deception of Hao Pu and capture of Guan Yu were the most brilliant. Though at first rash and bold and quick to kill without cause, in the end he mastered himself and had the capacity of a gentleman of national stature; how could he be merely a military commander? Chen Shou also recorded Sun Quan's assessment, saying it weighed merits and shortcomings fittingly. Records, Wu 9 §95