MGR was a member of the Congress Party till 1953 and he used to wear Khādī. In 1953 MGR joined the Dravida Munnetra Kazhagam (DMK) with the help ofM. Karunanidhi. He became a vocal Tamil and Dravidian nationalist and prominent member of the DMK] ("Dravida Munnetra Kazhagam" aka Dravidian Progressive Federation). He added glamour to the Dravidian movement which was sweeping Tamil Nadu. He became a member of the state Legislative Council in 1962. He was first elected to the Tamil Nadu Legislative Assembly in 1967. After the death of his mentor, Annadurai, MGR became the treasurer of DMK in 1969 after Karunanidhi became the chief minister.
On the 12th of January 1967, he was shot in the neck by fellow actor M.R. Radha.Both had worked together in 25 films together.When MGR was acting in the film Kaavalkaran in 1967 opposite Jayalalitha this incident happened.Petralthaan Pillaya was the last movie of MGR-MR Radha together, shooting which ended just few days before MGR was shot at.The bullet was permanently lodged in his neck and his voice damaged. Within hours of the shooting, some 50,000-odd fans had gathered at the hospital where MGR had been taken. People cried in the streets. For six weeks, he lay in the hospital as fans awaited each report of his health. He was visited by a steady stream of commoners and luminaries of film industry, polity and bureaucracy.From his hospital bed, he conducted his campaign for Madras Legislative Assembly. He won twice the number of votes polled by his Congress rival and the largest vote polled by any candidate for the Assembly.
In 1972, DMK leader Karunanithi started to project his first son M.K.Muthu in a big way in film industry and also in politics. Understanding the tactics played by Karunanithi to corner him, MGR started to claim that corruption had grown within the party after the demise of Annadurai and in a public meeting asked for the financial details of the party to be publicized which enraged the leadership of DMK. Consequently, as expected, MGR was expelled from the party, and floated a new party named Anna Dravida Munnetra Kazhagam (ADMK), later renamed All India Anna Dravida Munnetra Kazhagam (AIADMK), the only powerful opponent of the DMK.He mobilised the period between 1972-1977 to spread and preach his party ambiition with films like Netru Indru Naalai(1974), Idhayakani(1975) etc..,. He became Chief Minister of Tamil Nadu on the 30th of July 1977, remaining in office till his death in 1987. In 1979, members of his party Satyavani Muthu and Aravinda Bala Pajanor, became the first non-Congress politicians from Tamil Nadu to be ministers in the Union Cabinet. The AIADMK won every state assembly election as long as MGR was alive. Although Anna Durai as well as Karunanidhi had acted in stage plays in trivial roles, in their younger days, before becoming chief minister, MGR was the first popular film actor to be a Chief Minister in India.Though the Congress won by a small margin of votes with the DMK in the 1980 parliamentary elections, the AIADMK under MGR won the state elections the same year.This made the Congress to ally with the AIADMK in the 1984 elections.
Once he became Chief Minister of Tamil Nadu, he placed great emphasis on social development, especially education. One of his most successful policies was the introduction of the "Mid-day Meal Scheme" introduced by the popular Congress Chief Minister and Kingmaker K Kamaraj to a nutritious Mid-day Meal Scheme in the Government-run and aided schools in Tamil Nadu, which encouraged underprivileged children to attend schools. This scheme was at a cost of Rs.100 crore and was imposed in 1982. A little more than 12000000 citizns of the state were benefited. He also introduced Women's Special buses. He introduced Liquor ban in the state and Preservation of old temples and historical monuments, ultimately increasing the state's tourist income. He set up a free school for the Cinema Technicians children in Kodambakkam called MGR Primary & Higher Secondary School which provided Free Mid-Day meals in the 1950s. He led the ADMK to victory in the 1984 assembly elections despite not taking part in the campaigning. At that time he was undergoing medical treatment in America and his images were broadcast in Tamil Nadu through cinema halls. This was an effective campaign tactic and ADMK won the elections, indicating the depth of his popular support. He won the election in a double landslide victory in 1984.He still holds the record of being the chief minister with the highest consistent longevity of more than a decade.