Jayaprakash Narayan joined Bihar Vidyapeeth, founded by Dr. Rajendra Prasad for motivating young meritorious youths, and was among the first students of eminent Gandhian Dr. Anugrah Narayan Sinha, a close colleague of M.K. Gandhi who later became first Deputy Chief Minister cum Finance Minister of Bihar. In October, 1920 Jayaprakash married Prabhavati Devi, an independence activist in her own right and a staunch disciple of Kasturba Gandhi. Prabhavati was the daughter of lawyer and nationalist Brij Kishore Prasad, one of the first Gandhians in Bihar and one who played a major role in Gandhi's campaign in Champaran. She often held opinions which were not in agreement with JP's views, but Narayan respected her independence. On Gandhiji's invitation, she stayed at his Sabarmati Ashram while Jayaprakash continued his studies.

In 1922, Narayan went to the United States, where he worked to support his studies in political science, sociology and economics at the University of California, Berkeley, University of Iowa, University of Wisconsin – Madison and Ohio State University. He adopted Marxism while studying at the University of Wisconsin – Madison under sociologist Edward A. Ross; he was also deeply influenced by the writings of M.N. Roy. Financial constraints and his mother's health forced him to abandon his wish of earning a PhD. He became acquainted with Rajani Palme Dutt and other revolutionaries in London on his way back to India.

After returning to India, Narayan joined the Indian National Congress on the invitation of Jawaharlal Nehru in 1929; M.K. Gandhi became his mentor in the Congress. He shared the same house at kadam kuan in Patna with his close friend and nationalist Ganga Sharan Singh (Sinha) with whom he shared the most cordial and lasting friendship. During the Indian independence movement he was arrested, jailed, and tortured several times by the British. He won particular fame during the Quit India movement. After being jailed in 1932 for civil disobedience against British rule, Narayan was imprisoned in Nasik Jail, where he met Ram Manohar Lohia, Minoo Masani, Achyut Patwardhan, Ashok Mehta, Yusuf Desai and other national leaders. After his release, the Congress Socialist Party, or (CSP), a left-wing group within the Congress, was formed with Acharya Narendra Deva as President and Narayan as General secretary.

During the Quit India Movement of 1942, when senior Congress leaders were arrested in the early stages, JP, Lohia and Basawon Singh (Sinha) were at the forefront of the agitations. Leaders such as Jayaprakash Narayan and Aruna Asaf Ali were described as "the political children of Gandhi but recent students of Karl Marx." He was also a great advocate of co.relation "SAHJEEVAN".

Initially a defender of physical force, Narayan was won over to Gandhi's position on nonviolence and advocated the use of satyagrahas to achieve the ideals of democratic socialism. Furthermore, he became deeply disillusioned with the practical experience of socialism in Nehru's India.

After independence and the death of Mahatma Gandhi, Narayan, Acharya Narendra Dev and Basawon Singh (Sinha) led the CSP out of Congress to become the opposition Socialist Party, which later took the name Praja Socialist Party. Basawon Singh (Sinha) became the first leader of the opposition in the state and assembly of Bihar and Acharya Narendra Deva became the first leader of opposition in the state and assembly of U.P. His party is the first national party who distributed tickets on caste line.

On April 19, 1954, Narayan announced in Gaya that he was dedicating his life (Jeevandan) to Vinoba Bhave's Sarvodaya movement and its Bhoodan campaign, which promoted distributing land to Harijans (untouchables). He gave up his land, set up an ashram in Hazaribagh, and worked towards uplifting the village.

In 1957, Narayan formally broke with the Praja Socialist Party in order to pursue lokniti [Polity of the people], as opposed to rajniti [Polity of the state]. By this time, Narayan had become convinced that lokniti should be non-partisan in order to build a consensus based, classless, participatory democracy which he termed Sarvodaya. Narayan became an important figure in the India-wide network of Gandhian Sarvodaya workers.

In 1964, Narayan was vilified across the political spectrum for arguing in an article in the Hindustan Times that India had a responsibility to keep its promise to allow self-determination to the state of Jammu and Kashmir. He hit back at critics in a second article, dismissing the Indian version of the "domino theory" which held that the rest of India's states would disintegrate if Kashmir were allowed its promised freedom. In his graceful if old-fashioned style, Narayan ridiculed the premise that "the states of India are held together by force and not by the sentiment of a common nationality. It is an assumption that makes a mockery of the Indian Nation and a tyrant of the Indian State".

Narayan returned to prominence in State politics in the late 1960s. In 1974, he led the student's movement in the state of Bihar which gradually developed into a popular people's movement known as the Bihar movement. It was during this movement that JP gave a call for peaceful Total Revolution. Together with V.M. Tarkunde, he founded the Citizens for Democracy in 1974 and the People's Union for Civil Liberties in 1976, both NGOs, to uphold and defend civil liberties.

When Indira Gandhi was found guilty of violating electoral laws by the Allahabad High Court, Narayan called for Indira to resign, and advocated a program of social transformation which he termed Sampoorna kraanti [Total Revolution]. Instead she proclaimed a national Emergency on the midnight of June 25, 1975, immediately after Narayan had called for the PM's resignation and had asked the military and the police to disregard unconstitutional and immoral orders; JP, opposition leaders, and dissenting members of her own party (the 'Young Turks') were arrested on that day. Jayaprakash Narayan attracted a gathering of 100,000 people at the Ramlila Grounds and thunderously recited Rashtrakavi Ramdhari Singh 'Dinkar''s wonderfully evocative poetry: Singhasan Khaali Karo Ke Janata Aaati Hai. Narayan was kept as detenu at Chandigarh even after he had asked for a month's parole for mobilising relief in areas of Bihar gravely affected by flood. His health suddenly deteriorated on October 24, and he was released on November 12; diagnosis at Jaslok Hospital, Bombay, revealed kidney failure; he would be on dialysis for the rest of his life.

After Indira revoked the emergency on January 18, 1977 and announced elections, it was under JP's guidance that the Janata Party (a vehicle for the broad spectrum of the anti-Indira Gandhi opposition) was formed. The Janata Party was voted into power, and became the first non-Congress party to form a government at the Centre. On the call of Narayan many youngsters joined the J P movement.

He died in October 1979; but a few months before that, in March 1979, his death was erroneously announced by the Indian prime minister to the parliament as he lay fighting for his life in Jaslok Hospital, causing a brief wave of national mourning, including the suspension of parliament and regular radio broadcasting, and closure of schools and shops. When he was told about the gaffe a few weeks later, he smiled.