Li Yifu was born in 614, during the reign of Emperor Yang of Sui, and his clan was originally from what would become Ying Prefecture (瀛州, part of modern Cangzhou, Hebei), but as his grandfather served as the secretary to the county magistrate of Shehong County (射洪, in modern Suining, Sichuan), his family stayed in the area thereafter.
Emperor Gaozong and Consort Wu were pleased, and they promoted Li Yifu to be the assistant head of the legislative bureau.
After Emperor Gaozong did depose Empress Wang and replace her with Consort Wu later that year, over the strenuous objections of the chancellors Chu Suiliang, Han Yuan, and Lai Ji and implicit disapproval of Zhangsun, Li Yifu was given the designation of Canzhi Zhengshi (參知政事), making him a chancellor de facto.
Li Yifu had the secretary general of the supreme court, Bi Zhengyi (畢正義), improperly find her not guilty and release her, with the intent that he would then take Lady Chunyu as a concubine.
(Liu Ji had been forced to commit suicide around the new year 646 due to accusations that he had planned to kill a number of high level officials disagreeing with him if Emperor Taizong had died from a serious illness that he was suffering from at the time.)
In 657, Li Yifu was made Zhongshu Ling (中書令), the head of the legislative bureau and an office considered one for a chancellor.
Later that year, he, and another ally of Empress Wu's, Xu Jingzong, falsely accused Chu, Han, and Lai of conspiring to commit treason, and both Han and Lai (who were still chancellors) were demoted out of the capital to be prefects, while Chu and Empress Wang's uncle Liu Shi were demoted to be prefects of exceedingly distant prefectures.
Around the new year 659, Tang Lin (唐臨), the minister of civil service affairs, had submitted suggestions that Xu Hui (許褘) be made the examiner of the Jiangnan Circuit (江南道, region south of the Yangtze River) and Zhang Lun (張倫) be made the examiner of the Jiannan Circuit (劍南道, modern Sichuan, Chongqing, and Yunnan).
In fall 659, Emperor Gaozong recalled Li Yifu to the capital, to serve as the minister of civil service affairs and de facto chancellor.
Emperor Gaozong thus issued an edict forbidding the seven most prominent clans from marriage with each other and also limiting the amount of dowry and bride price they are permitted to receive.
In 661, Li Yifu's mother died, and he resigned to observe a period of mourning for her, but was recalled in 662 to again serve as minister of civil service affairs and chancellor de facto.
In 663, Li Yifu was made the head of the legislative bureau (by now known as You Xiang (右相)), but continued to be in charge of civil service.
Eventually, Emperor Gaozong heard about this, and on one occasion, still calmly stated to Li Yifu: "Your sons and sons-in-law are careless, and they have committed many unlawful acts.
Meanwhile, an astrologer Li Yifu trusted, Du Yuanji (杜元紀), informed him that there was an aura of imprisonment at his house, and that he could only suppress it by a large store of money.