Triple talaq divorce is legal under the Indian constitution, which allows the country's 1.2 billion citizens to be governed by their own religious laws when it comes to marriage, divorce and property inheritance.
The practice has faced repeated legal challenges in recent years, and Modi's Hindu nationalist government has said it wants to replace it with a new uniform civil code applicable to all religious groups.
But that proposal has met stiff opposition from Muslim groups, who argue that it would discriminate against them.
"What is the crime of my Muslim sister that just like that over the telephone someone says 'talaq' three times and her whole life should be ruined?" Modi said at a rally in the northern state of Uttar Pradesh.
"No injustice should be meted out to our mothers and sisters in the name of religion or community," he said in the televised speech.
Uttar Pradesh is India's most populous state and 20 percent of its 200 million people are Muslim.
Modi, whose Bharatiya Janata Party is gearing for state elections there early next year, said it was his government's duty to ensure the rights of Muslim women were upheld.
"We should not look at religion when it comes to respecting or protecting women," said Modi.
"Election, votes, politics must be kept on one side: Muslim women must get their rights."
Some Indian Muslim women have in recent years launched legal challenges to triple talaq, which they say discriminates against them and violates their human rights.
A case in the mid-1980s involving Muslim woman Shah Bano, who took her rejected demand for alimony to the Supreme Court, triggered debate across India about whether the court had authority over Muslim personal law.
The court upheld her right to alimony, but its verdict was reversed by a law passed by the then-Congress party government after Muslim groups reacted angrily.
The Supreme Court is currently hearing a petition filed by women's rights activists who want the judiciary to declare triple talaq unconstitutional.
Muslims make up more than 13 percent of the population of India, a secular democracy with a Hindu majority.
