In India, Republic Day honours the date on which the Constitution of India came into force replacing the Government of India Act 1935 as the governing document of India on 26 January 1950. -Wikipedia
Indian independence movement noted for largely peaceful nonviolent resistance and civil disobedience led by the Indian National Congress. The independence came through the Indian Independence Act 1947 (10 & 11 Geo 6 c. 30), an Act of the Parliament of the United Kingdom that partitioned British India into the two new independent Dominions of the British Commonwealth (later Commonwealth of Nations): India and Pakistan. India obtained its independence on 15 August 1947 as a constitutional monarchy with George VI as head of state and the Earl Mountbatten as governor-general. The country, though, did not yet have a permanent constitution; instead its laws were based on the modified colonial Government of India Act 1935. On 28 August 1947, the Drafting Committee was appointed to draft a permanent constitution, with Dr.B. R. Ambedkar as chairman. While India's Independence Day celebrates its freedom from British Rule, the Republic Day celebrates the coming into force of its constitution.
A draft constitution was prepared by the committee and submitted to the Assembly on 4 November 1947. The Assembly met, in sessions open to public, for 166 days, spread over a period of 2 years, 11 months and 18 days before adopting the Constitution. After many deliberations and some modifications, the 308 members of the Assembly signed two hand-written copies of the document (one each in Hindi and English) on 24 January 1950. Two days later, it came into effect throughout the nation.