It is not known when Wu Sansi was born. His father Wu Yuanqing was a half-brother of Wu Zetian -- both had, as father, the early Tang Dynasty general Wu Shihuo , but Wu Yuanshuang and his brother Wu Yuanshuang were born of Wu Shihuo's first wife Lady Xiangli, while Wu Zetian and her two sisters were born of Wu Shihuo's second wife Lady Yang. After Wu Zetian became empress to in 655, despite previous intrafamily unpleasantries -- Wu Yuanqing and Wu Yuanshuang, as well as Wu Shihuo's nephews Wu Weiliang and Wu Huaiyun were often disrespectful of Lady Yang previously -- Empress Wu's brothers and cousins were often promoted by Emperor Gaozong, with Wu Yuanqing promoted to ''Zongzheng Shaoqing'' , the deputy minister of imperial clan affairs. However, sometime before 666, Empress Wu, angry that her brothers and cousins did not appreciate the promotions, had them all demoted, with Wu Yuanqing demoted to be the prefect of Long Prefecture . After he arrived at Long Prefecture, he, in fear that Empress Wu had further retaliation in the works, died. It is not completely clear, but it was likely that Wu Sansi went to Long Prefecture with his father Wu Yuanqing. He was later made a commanding general of the imperial guards.
During Emperor Zhongzong's and Emperor Ruizong's first reigns
Emperor Gaozong died in 683, and was initially succeeded by his and Empress Wu's son the Crown Prince , but Empress Wu retained power as empress dowager and regent. In spring 684, after Emperor Zhongzong showed signs of independence, she deposed him and replaced him with another son, the Prince of Yu, but wielded power even more tightly thereafter. Sometime during her regency, Wu Sansi became minister of defense . Both he and his cousin Wu Chengsi advised Empress Dowager Wu to find excuses to kill two senior members of the imperial Li clan -- Emperor Gaozong's uncles Li Yuanjia the Prince of Han and Li Lingkui the Prince of Lu due to their senior status. Wu Sansi and Wu Chengsi were also said to be often advocating that Empress Dowager Wu take over the throne herself as "emperor."
In [, Wu Sansi was given the designation ''Tong Fengge Luantai Sanpin'' , making him a chancellor ''de facto'', but about a month later, he was stripped of the chancellor designation. It was said that he and Wu Chengsi both had designs on being crown prince, and often had their associates try to persuade Wu Zetian that in ages past, there had never been an emperor who had, as his heir, someone with a different family name. In 698, however, at the suggestion of the chancellor Di Renjie, concurred in by Wang Jishan and Wang Fangqing, as well as Wu Zetian's close advisor Ji Xu and her lovers Zhang Yizhi and Zhang Changzong, Wu Zetian recalled Li Zhe the Prince of Luling from exile and soon, after Li Dan offered to yield the position of crown prince to him, created him crown prince and changed his name to Li Xian and then to Wu Xian.
During Emperor Zhongzong's second reign
Wu Zetian was overthrown in a coup in 705 led by the officials Zhang Jianzhi, Cui Xuanwei, Jing Hui, Huan Yanfan, and Yuan Shuji. Zhang Yizhi and Zhang Changzong were killed in the coup, and Emperor Zhongzong was restored to the throne; Wu Zetian was sent to a secondary palace under heavy guard, and while she also retained the title of "emperor," no longer had power. By that time, Wu Sansi had been carrying out an affair with Wu Zetian's secretary and Emperor Zhongzong's concubine . Through her introduction, Wu Sansi began an affair with Emperor Zhongzong's wife as well and also became a trusted advisor to Emperor Zhongzong who, while he was restored through the efforts of Zhang Jianzhi and his colleagues, feared them. In addition, Wu Sansi's son Wu Chongxun had been married to Emperor Zhongzong's and Empress Wei's daughter Li Guo'er the Princess Anle, who also had much power in her father's administration.
Meanwhile, the coup leaders initially did not of Wu Sansi as a threat, and they brushed aside suggestions by two lower level officials participating in the coup, Xue Jichang and Liu Youqiu. However, they soon realized that Wu Sansi's power was on the rise, and they unsuccessfully suggested Emperor Zhongzong to kill some of the more powerful Wu clan members or to demote them -- and indeed, he made Wu Sansi ''Sikong'' and chancellor again with the designation ''Tong Zhongshu Menxia Sanpin'' , although Wu Sansi declined the titles. Meanwhile, Emperor Zhongzong designated 16 officials, including the coup leaders but also Wu Sansi and his cousin Wu Youji , as contributors to his return to the throne and gave them iron certificates that were supposed to guarantee that they would be spared of death penalties 10 times except for treason.
Jing, fearful of Wu Sansi's power, retained the mid-level official Cui Shi to watch for Wu Sansi's moves -- but Cui Shi, realizing that Emperor Zhongzong trusted Wu Sansi and feared the coup leaders, instead became Wu Sansi's associate, along with Zheng Yin, who suggested that Wu Sansi find some way to remove the five coup leaders, now all chancellors, from their posts. Wu Sansi and Empress Wei, in turn, argued to Emperor Zhongzong that the five coup leaders were overpowering in the government and should be given honorific titles but be removed from office. At their suggestion, Emperor Zhongzong created the five coup leaders princes and awarded them much wealth, but removed them from governmental posts, including chancellor positions -- and soon sent Zhang Jianzhi and Cui Xuanwei out of the capital. Wu Sansi, now in power, had much of Wu Zetian's policies, which the five coup leaders had reversed, reinstated. Meanwhile, to diffuse some of the popular sentiment against the Wu clan, Emperor Zhongzong demoted their titles slightly, and Wu Sansi's title was reduced from Prince of Liang to the lesser title of Prince of Dejing. As Emperor Zhongzong also trusted Wei Yuanzhong , when Wu Zetian died in late 705, Wu Sansi tried to ingratiate Wei by writing into Wu Zetian's will a provision giving Wei an additional fief of 100 households. Wei, in gratitude, did not oppose the Wu clan further from that point.
In spring 706, Wu Sansi, fearful that Jing, Huan, and Yuan were still in the capital, sent them out of the capital to serve as prefectural prefects. Meanwhile, an incident occurred that allowed Wu Sansi to act further against the five coup leaders -- as Emperor Zhongzong's son-in-law Wang Tongjiao , himself a participant in the coup, was accused of plotting with Zhang Zhongzhi , Zu Yanqing , and Zhou Jing to kill Wu Sansi and deposing Empress Wei. The alleged plotters were all killed, and Wu Sansi and Empress Wei thereafter accused the five coup leaders of having been part of Wang Tongjiao's plot, and the five were demoted further, to more distant prefecture, with no possibility of return from exile. Meanwhile, Wu Sansi, knowing that Emperor Zhongzong was very sensitive about any accusation of adultery by Empress Wei, intentionally had people post public accusations that she had been involved in adultery -- and then framed the five coup leaders of doing so, and the five coup leaders, already in exile, were stripped of all of their titles and honors. Wu Sansi, at Cui Shi's suggestion, then sent the secret police official Zhou Lizhen to the Lingnan region, where the five had been exiled, to survey the area, but with instructions to have the five killed. When Zhou reached Lingnan, Zhang Jianzhi and Cui Xuanwei had already died, but he killed Huan, Jing, and Yuan in cruel manners. It was said that after news of the five coup leaders' deaths reached Wu Sansi, he commented, "I do not know who are good people and who are bad people on this earth. I only know that people who are good to me are good, and people who are bad to me are bad."
Meanwhile, Emperor Zhongzong had created his son Li Chongjun, by a concubine, crown prince, as Empress Wei's only son Li Chongrun had been killed by Wu Zetian in 701, but Li Guo'er, encouraged by Wu Chongxun, had designs on becoming crown princess, and repeatedly asked Emperor Zhongzong to make her crown princess. Both she and Wu Chongxun also repeatedly insulted Li Chongjun, sometimes calling him "slave." In fall 707, Li Chongjun, in anger, started a rebellion with the generals Li Duozuo, Li Sichong , Li Chengkuang , Dugu Yizhi , and Shazha Zhongyi , as well as Emperor Zhongzong's cousin Li Qianli the Prince of Cheng and LI Qianli's son Li Xi the Prince of Tianshui. They attacked Wu Sansi's mansion and killed Wu Sansi, Wu Chongxun, and some of their relatives. Li Chongjun's subsequent attempt to reach the palace and arrest Consort Shangguan, Empress Wei, and Li Guo'er, however, were unsuccessful, and his troops collapsed; he was killed. Li Chongjun was beheaded, and his head was presented to Wu Sansi's and Wu Chongxun's caskets. Wu Sansi and Wu Chongxun were buried in grand funerals, and Wu Sansi was posthumously recreated the Prince of Liang with the posthumous name of Xuan . After Emperor Zhongzong's death in 710, a coup lead by Princess Taiping and Li Dan's son the Prince of Linzi overthrew Empress Wei and restored Emperor Ruizong to the throne, and Wu Sansi's tomb was destroyed.