President Ram Nath Kovind on Thursday gave his assent to the Citizenship (Amendment) Bill, 2019, turning it into an Act. The contentious law promises citizenship to migrants from three neighbouring countries but not if they are Muslims.
According to an official notification, the law comes into effect with its publication in the official gazette on Thursday.
According to the Act, members of Hindu, Sikh, Buddhist, Jain, Parsi and Christian communities who have come from Pakistan, Bangladesh and Afghanistan till December 31, 2014 and facing religious persecution there will not be treated as illegal immigrants but given Indian citizenship.
The Citizenship (Amendment) Bill was passed by Rajya Sabha on Wednesday and by Lok Sabha on Monday after fiery debates.
Prime Minister Narendra Modi's BJP government has said the Citizenship Bill was meant to protect minorities who faced persecution in the neighbouring countries.
The bill has triggered massive protests in the northeast. Violent mobs in Assam torched buildings and clashed with police on Thursday, leaving at least two dead. A curfew was also to be imposed in parts of the capital city of the neighbouring state of Meghalaya, a government official said, because of fears of the law and order situation deteriorating.
The protesters in Assam, which shares a border with Bangladesh, say the measure would open the region to a flood of foreign migrants.
Opposition parties, however, said the bigger problem with the new law was that it undermined India's secular constitution by not offering protection to Muslims.
Prime Minister Narendra Modi Modi urged calm and said the people of Assam had nothing to fear. "I want to assure them - no-one can take away your rights, unique identity and beautiful culture. It will continue to flourish and grow," he tweeted.
The government has said the new law will be followed by a National Register of Citizens that means Muslims must prove they were original residents of India and not refugees from these three countries. Members of other faiths listed in the law, by contrast, have a clear path to citizenship.
(With inputs from Agencies)