Born in Houma, Shanxi province, Peng was originally named Fu Maogong (傅懋恭). He joined the Chinese Communist Party (CCP) in 1923 as a founding member of the Shanxi Province CCP. Arrested in 1929, he continued underground political activities while imprisoned. He was released from prison in 1935 and began organizing a resistance movement against the invading Japanese forces. Peng was important in developing the Second United Front during the Second Sino-Japanese War.^[1]: 145 Around the same time, he was appointed the Organization Department Director of the North Bureau of CCP.

Peng also served on a number of positions as vice-president of the Central Party School and director of the CCP Policy Research Office. In 1945 he served in the history research committee and the organizing committee of the CCP's 7th National Congress.

In September 1945 Peng was sent by Mao Zedong to take up overall leadership of the CCP in Northeast China. He was accompanied by Lin Biao who was to assist Peng with directing military operations against the Nationalists. Peng decided that the CCP could hold the 3 big cities of the Northeast: Shenyang, Changchun and Harbin. When the Nationalists under the command of Du Yuming attacked in November 1945, the Communists were forced back. Peng was removed as the CCP leader in the northeast after further failure by Lin Biao's forces in March 1946 led to the Communists retreat back to Harbin.^[2]

Peng was a member of the CCP Central Committee starting from 1944 as well as a member of the Secretariat of the CCP Central Committee. He also held the positions of First Secretary of the Beijing Municipal Committee, and Mayor of Beijing from 1951 to 1966. In addition to being mayor, he was a high-ranking member of the Politburo from 1956 to 1966.

In June 1958, Mao changed the party and government structure by establishing groups in charge of finance, legal matters, foreign affairs, science, and culture and education which bypassed the State Council.^{[3]: 414–415} Peng was made the head of the legal matters group.^[3]: 415

In June 1960, he attended Bucharest Conference of Representatives of Communist and Workers Parties, in which he rebutted Soviet leader Nikita Khrushchev after he criticized Mao.^[4]

During the Seven Thousand Cadres Conference in 1962, Peng along with other establishment figures criticized Mao for his "mistakes" over the disastrous outcome of the Great Leap Forward.^[4]

In the early 1960s, a prominent historian named Wu Han had written a stage play Hai Rui Dismissed from Office, which Mao took it as an allegory to a former Defense Minister who had been purged by Mao in 1959 for having opposed him during the Great Leap Forward. By 1965, Wu had been promoted to deputy mayor of Beijing under Peng, who was an ally of President Liu Shaoqi. Mao decided that Peng would be the key in his ultimate plan to purge Liu, who was increasing falling out of favor with Mao after Liu defied the Chairman's policies in the Seven Thousand Cadres Conference.^[4]

On Mao's instructions, a article written by one of Mao's associates appeared in the Shanghai-based newspaper Wenhui Bao and attacked Wu for having written the play to indirectly criticize Mao's decision for purging the former Defense Minister and sought for his political rehabilitation. Peng ordered the Beijing-based newspapers as well as the Party's mouthpiece People's Daily not to reprint the article, which angered Mao, who later accused Peng of running an "independent kingdom" in Beijing.^[4]

Before the incident, Peng was appointed head of the Five Man Group in charge of preparing a "cultural revolution", and approved new guidelines in February 1966 for dealing with ideological disputes, known as the "February Outline", which affirmed that a "gigantic struggle was underway between Mao Zedong Thought and bourgeois ideas", to which Mao neither approved nor objected to Peng's proposal at that time. Peng acknowledged to Mao that Wu had committed political errors, but it should be resolved through scholarly means.^[4]

In April 1966, Mao decided to attack Peng. Peng's "Outline" was annulled on the grounds that it "obscured class lines", and Mao denounced Peng as a "Party tyrant" who had protected "scholar tyrant" Wu Han. Peng had also been in charge of the cultural sphere since July 1964, and Mao approved a document drawn up by his wife, Jiang Qing during a cultural forum that claimed those who were involved in the cultural sphere prior were "black elements", which implicated Peng. He was accused of being an associate to Wu Han's counter-revolutionary clique, deposed along with his associates Lu Dingyi, Luo Ruiqing and Yang Shangkun and the Five Man Group was replaced by a specialized Leading Group led by Jiang Qing at a May 1966 conference in what became the opening act of the Cultural Revolution.^[4]

Peng was removed from his positions as First Secretary of the Beijing Municipal Committee and Mayor of Beijing and his Politburo membership was stripped. Peng along with his former colleagues in the Municipal Committee were publicly struggled against at mass rallies in sports stadiums and gymnasiums, with them standing or kneeling and wearing placards around their necks bearing the words "Counter-revolutionary Revisionist" while Red Guards yanked back their hairs and forced them to bow to an angry crowd. Peng was struggled against at least 53 times during the Cultural Revolution.^[4]

Peng survived the Cultural Revolution, and was eventually rehabilitated under Deng Xiaoping. In February 1979, he headed the newly-established Legal Affairs Commission of the Standing Committee of the National People's Congress. Consisting of 80 legal officials, the office was given autonomy by the CCP to draft laws.^[5] In what was termed as a "miracle", the commission drafted and submitted seven bills in three months.^[6]

Peng subsequently became Secretary of the Central Political and Legal Affairs Commission, a post he already held from late 1950s in the capacity of leader of a Central Politics and Law Leading Group. Beginning in 1983, as Chairman of the Standing Committee of the 6th National People's Congress, he sought to increase the NPC's power. He used the NPC as a base to oppose reform.^[7]: 196 In January 1987, Peng Zhen played a pivotal role in Hu Yaobang's resignation as General Secretary by attack and criticizing Hu during a meeting. Peng left Politburo after the 13th Party Congress in November 1987 and retired from politics in March 1988 after Wan Li took over his position as Chairman of NPC Standing Committee. During the 1989 Tiananmen Square protests, Peng Zhen supported the declaration of martial law in Beijing and the removal of Zhao Ziyang.

Peng Zhen died on April 26, 1997, from blood cancer aged 94, two months after the death of former vice premier Deng Xiaoping, and was eulogized with high honours by the highest organs of the party and the state. His official obituary declared him a "great proletarian revolutionary, politician, and outstanding expert in the affairs of the state; unswerving Marxist, instrumental in laying the foundations of legal institution in our country, and excellent leader of the party and state." The obituary also curiously made mention of his support of Deng Xiaoping's 1992 "southern tour" which re-ignited economic reforms after relative stagnation following the 1989 Tiananmen Square protests.^[8]

He was considered one of the Eight Elders of the CCP.^{[citation needed]}