The Constitution of India was fully written and adopted by the Constituent Assembly on November 26, 1949, but the major part of the Constitution came into force only on January 26, 1950, making India a republic.
Although the date of adoption of the Constitution is November 26, 1949, the process of drafting the Constitution took a lot longer. The Constituent Assembly took about 2 years, 11 months and 18 days to prepare the draft.
The final version of the Constitution was signed by the members of the Assembly on January 24, 1950. The Constitution of India officially came into force on January 26, 1950.