Who Was Appointed as the Legal Advisor to the Constituent Assembly
The first case is seen when Rau was appointed Special Service Officer (SOO) in the Viceroy`s Reform Bureau to facilitate the implementation of the Government of India Act passed in 1935. As readers will recall, the Act required the British government to delegate the direction of provincial governments to Indian representatives elected by the people of those provinces. After his appointment, however, Rau noted that in practice the various departments of the British government in the provinces were somewhat reluctant to delegate such powers. His outstanding work earned him the title of Companion of the Order of the Indian Empire (CIE) in the New Year`s Honours List in 1934 and a distinction in 1938. Rau retired in 1944 and was subsequently appointed Prime Minister of the princely state of Jammu and Kashmir.  He resigned from this post in 1945 after differences with the then Maharaja of Kashmir and wrote in his resignation letter that «. I have known for some time that we disagree on some fundamental foreign and domestic policy issues. And this, as it should be, leads to disagreements on many details. I have never questioned, and I do not question, the position that Your Highness` decision must be final in all these matters. The Prime Minister must either accept it or resign.  B. N. Rau was appointed constitutional adviser to the Constituent Assembly in 1946 when the Indian Constitution was drafted.
 He was responsible for the general structure of the democratic framework of the constitution and prepared his first draft in February 1948.  This project was approved on July 26. It was discussed, revised and finally adopted by the Constituent Assembly of India in November 1949.  Rau`s work as constitutional adviser proved extremely useful to the Constituent Assembly. His expertise not only in British constitutionalism, but also in the functioning of constitutions around the world greatly assisted members of the Constituent Assembly in finding an appropriate reference for various constitutional provisions. Indeed, a striking feature of the draft constitution that Rau prepared for members was the notes in the margins indicating the origin of these provisions from other countries. This is one of the ways in which the drafting of the Indian constitution was not only a national enterprise, but became fundamentally global in nature. Therefore, Rau`s role was crucial and crucial to India`s transition from a colony to an independent state through the constitution.
Rau has served India as a representative delegate to the United Nations. From 1949 to 1952, he served as Permanent Representative of India to the United Nations until he was appointed a judge at the International Court of Justice in The Hague. In June 1950, he became President of the United Nations Security Council.  With the resolution of the Constituent Assembly of August 29, 1947, the Drafting Committee was established under the chairmanship of B. R. Ambedkar stated that it would be established to «examine the draft constitutional text prepared by the constitutional adviser, to give effect to the decisions already taken in the assembly, and to include all matters related to or to be provided for in such a constitution, and submit to the Assembly for consideration the text of the draft constitution as revised by the Commission». The draft prepared by the Constitutional Adviser was presented in October 1947. With this draft, the proposals of the various other commissions created by the Constituent Assembly were taken into account. The first draft of the editorial board was published in February 1948. The Indian people have had eight months to discuss the project and propose changes. In light of public comment, criticism and suggestions, the editorial board prepared a second draft, which was published in October 1948. The final draft of the Constitution was drafted by Dr.
B. R. Ambedkar on November 4, 1948 (first reading). The second reading was considered article by article and lasted more than a year. After three drafts and three readings, the Constitution was declared adopted on 26 November 1949. Dr. B. R. Ambedkar stated in his closing address to the Constituent Assembly on November 25, 1949: After his resignation as Chief Minister of Kashmir, Rau was invited to serve temporarily in the Reform Bureau of the Government of India, which he did. He was also offered the position of permanent judge of the Supreme Court of Calcutta, and he preferred to remain in the Bureau of Reform and work on constitutional and federal matters. He was then appointed secretary to the Office of the Governor General and worked on constitutional reforms until he became constitutional adviser to the Constituent Assembly in 1946.  Rau`s inclination towards constitutional issues became evident from the beginning. He developed a keen interest in legislative and constitutional affairs, which led to his appointment as a Legal Memoir and Secretary to the Government of Assam in the Legislative Department and Council.
From 1935, Rau was at the centre of major constitutional developments in India.