No person shall be a citizen of India by virtue of article 5, or be deemed to be a citizen of India by virtue of article 6 or article 8, if he has voluntarily acquired the citizenship of any foreign State.
Article 9 bars dual citizenship.
Article 9 was initially a proviso to Article 5 of the Constitution. In the Assembly it was debated as a part of Article 5. During the revision stages, the Drafting Committee believed that bar on dual citizenship must be a general principle and not be restricted to conditions under Article 5.
During the Constituent Assembly debates, one member argued in favour of dual citizenship. He noted that it should be limited to countries which extend the same to Indians. But this was not discussed and finally the Assembly voted against this proposal.