He began his high school education at Tangshan Number 1 High School in 1905. From 1913 to 1917 Li studied political economy at Waseda University in Japan before returning to China in 1918.
Returning to Peking (now Beijing) in the summer of 1916, he became editor of the Ch'en Pao (Morning Post). In February 1918 Li became chief librarian at National Peking University (Peita) and in 1920 was named professor of history, economics, and political science. At Peita he was swept up in the intellectual currents of the New Culture movement and became a member of the editorial board of the influential Hsin ch'ing-nien (New Youth) magazine. In December 1918 he and Ch'en Tu-hsiu founded the Mei-chou p'ing-lun (Weekly Critic) as an outlet for political protests against Tuan Ch'i-jui's warlord government. Li exercised a profound personal influence on the students at Peita. His study at the library became a gathering place for political groups. Always ready to help young men in need, he found a place as clerk in the library for an indigent Hunanese named Mao Tse-tung. Li threw himself into the activities of student protest following the seminal demonstration of May 4, 1919, against the sellout of Shantung to Japan. Li was unable to attend the founding congress of the Chinese Communist party (CCP) in July 1921, but the second congress a year later elected him to the party's Central Committee. At a special plenum of the committee in August 1922, Li supported the proposal of Comintern agent Maring advocating alliance with the Kuomintang, and Li was the first Communist to become a Kuomintang member. However, his efforts to extend the alliance to the presumably progressive warlord Wu P'eifu were brusquely terminated in February 1923, when Wu crushed the Peking-Hankow railroad strike. In January 1924 Li was elected to the Central Executive Committee of the Kuomintang and to the Central Executive Committee of its Peking branch; later he attended the fifth congress of the Comintern in the U. S. S. R. Following a period of seclusion to avoid arrest by Wu P'ei-fu, Li returned to Peita to continue his pedagogical and political activities. Though reelected to the Kuomintang's Central Executive Committee in January 1926, he found his position in Peking increasingly tenuous. On March 18, 1926, he barely escaped with his life when police opened fire on a demonstration he had organized to protest imperialistic encroachments on China's sovereignty. Under increasing pressure from northern warlords, he was frequently driven to seek refuge in the Soviet embassy. There he was arrested on April 6, 1927, by the forces of Chang Tso-lin. On April 28 he and 19 comrades were executed. Unlike his colleague Ch'en Tu-hsiu, Li died without falling victim to the internecine turmoil that soon rent apart the leadership of the CCP. Unlike Ch'en, who is anathematized as a "right opportunist" in Chinese Communist annals, Li remains honored as a founding father of the Chinese Communist movement.
Li developed a serious interest in Marxism. His article "The Victory of Bolshevism" (October 1918) hailed the revolution in Russia. He organized a Marxist research society (1918) and a society for the study of Marxism (1920) and edited a special issue of Hsin ch'ing-nien on Marxism (May 1919). Li soon became involved in the formation of a Communist nucleus. The catalyst for this activity was Gregory Voitinsky, a Comintern agent whom Li had sent to Shanghai with an introduction to Ch'en Tu-hsiu. Following discussions with Voitinsky, Ch'en organized a party nucleus; Li soon followed in his footsteps. Thanks to his popularity among student activists, Li was able to attract into the party a number of talented youths who subsequently gained political renown. In line with his populist inclinations, Li encouraged students to go to the workers and peasants.
Li was elected to the KMT's Central Executive Committee in 1924.