In April 1936, Babuji became a member of the Bihar Legislative Council. Meanwhile, elections under the Government of India Act, 1935 were scheduled to be held in 1936-37. Such was Babuji's political acumen and his stature that no one filed their nomination against him. In December 1936 itself, Babuji was elected unopposed to the Bihar Legislative Assembly as a candidate of the Bhartiya Depressed Classes League (BDCL), his own Organization. He also ensured unopposed victory of 14 other candidates of BDCL from reserved constituencies. He was then just 28 years old. Thereafter, on the invitation of Congress, he joined Congress with his 14 MLAs.

It was in the year 1946 that he assumed the office of the Minister of Labour in the Interim Government at the Center having been elected unopposed as a Congress candidate. He was the youngest member in the 2 interim governments. In the post-independence India, he won all the Lok Sabha elections-1952, 1957 (Unopposed), 1962, 1967, 1971, 1977, 1980, 1984 from the same constituency of Sasaram. People of Sasaram were like his family. He was always there for them. They too, in turn, always stood by him. He brought glory to Sasaram the way Sher Shah Suri had once done. From 1936, until his death in 1986, his uninterrupted Parliamentary career of half a century is a world record.

When it became clear that the independence of India could not be delayed for long, the British rulers decided to form an Interim Government, to which they could transfer power. On 2 September 1946, an Interim Government under Lord Wavell, was constituted in Delhi. On 30 August 1946, the Emperor of India, George VI, wrote to Babuji inviting him to join the Executive Council of the Interim Government. He was the sole representative of the Dalits in that Government. The following were the Members of the Interim Government:-

He had an unparallel record of serving as the Minister and Deputy Prime Minister in the Central Cabinet for 31 years. With his awesome administrative ability, he not only successfully met the challenges of nation building, but also streamlined the ministries he held.

Pre-Independence
Labour Minister - 2 September 1946 to 15 August 1947.

Post-Independence
Labour Minister - 15 August 1947 to 13 May 1952.
He framed many landmark legislations such as Industrial Disputes Act, 1947; Minimum Wages Act, 1948; Employees State Insurance Act, 1948; Labour Act, 1951; Employees Provident Fund Act, 1952, etc. He was the first Indian Labour Minister to preside over the International Labour Organization meet in Geneva.

Communication Minister - 13 May 1952 to 7 December 1956.
In 1953, he nationalized private airlines and established Indian Airlines Corporation and Air India International. He also extended the network of post, telegraph and telecommunication to remote village areas.

Rail and Transport Minister - 7 December 1956 to 17 April 1957.
He reviewed the old regulations and improved the service conditions of railways and transport employees.

Railway Minister - 17 April 1957 to 10 April 1962.
He modernized the railways and extended its network to different parts of the country. 1n 1957, orders for reservation in promotion for Scheduled Castes and Scheduled Tribes were issued for the first time.

Transport and Communication Minister - 10 April 1962 to 31 August 1963.
Metrology was used for the first time in river valley projects, irrigation projects and in the navy. Scholarship was offered for the first time for pilot training in flying clubs. Calcutta, Haldia, Madras, Vishakhapatnam, Kandla Ports were extensively extended. State level roads were converted into national highways on a large scale.

To strengthen the Indian National Congress, he resigned from the Government under the Kamraj Plan on 31 August 1963.

Labour, Employment & Rehabilitation Minister 24 January 1966 to 13 March 1967.
For providing security to the workers serving in mines and related fields, he framed the Mines Vocational Training Rules, 1966. He reviewed the old labour laws and implemented them in a more effective manner.

Food, Agriculture, Community Development & Cooperative Minister - 13 March 1967 to 27 June 1970.
Facing the most severe drought of 1967 with firm determination, he ensured that nobody died of hunger. He launched the 'grow more crops scheme' and brought about the 'Green Revolution'. Our country not only became self sufficient in food grains for the first time but also started its export.

Additional Charge of Labour, Employment & Rehabilitation Ministry - 15 November 1969 to 18 February 1970.
He enforced the labour laws strictly.

Defence Minister - 27 June 1970 to 10 October 1974.
As Defence Minister, he ensured historical victory in the Indo-Pak war, due to which Bangladesh was created. It was for the first time that India won a war. He provided liberal financial support and better employment opportunities to the wounded and the families of the martyrs.

Food, Agriculture and Irrigation Minister - 10 October 1974 to 2 Februrary 1977.
To improve the deteriorating food front, he again took charge of the Food and Agriculture Ministry. He settled the international water disputes over distribution of river Ganga waters with Bangladesh. At the national level, disputes over the distribution of the Ganga water were settled between different States. He also set up a Commission to settle future disputes.

Defence Minister - 28 March 1977 to 24 January 1979.
He inducted the modern, sophisticated fighter aircraft Jaguar in the Air Force. He improved the service conditions of the Army, Air and Naval personnel and provided them better pay and facilities.

No Cabinet Minister or Deputy Prime Minister has had such a long tenure.