Under the deal, India has committed to ensuring that at least 40% of its electricity will be generated from non-fossil sources by 2030.
CO2 emissions are believed to be the driving force behind climate change.
Last December in Paris, countries agreed to cut emissions in a bid to keep the global average rise in temperatures below 2C.
The Paris deal is the world's first comprehensive climate agreement.
It will only come into force legally after it is ratified by at least 55 countries which between them produce at least 55% of global carbon emissions.
Prime Minister Narendra Modi announced last month that India would ratify the agreement on 2 October, the birthday of Mahatma Gandhi, the leader of the struggle for independence from Britain.
"India has deposited its instrument of ratification of the Paris Agreement with the United Nations," the UN said in a statement on Sunday.
The US and China - together responsible for 40% of the world's carbon emissions - both formally joined the Paris global climate agreement earlier this month.
India accounts for about 4.5% of global greenhouse gas emissions, and became the 62nd country to ratify the agreement.
The European Union is expected to do so in the near future, taking approvals past the 55% of emissions threshold.
Paris agreement: Key points
- To keep global temperature increase "well below" 2C and to pursue efforts to limit it to 1.5C
- To peak greenhouse gas emissions as soon as possible and achieve a balance between sources and sinks of greenhouse gases in the second half of this century
- To review progress every five years
- $100bn a year in climate finance for developing countries by 2020, with a commitment to further finance in the future
- Once the deal comes into force, countries that have ratified it have to wait for a minimum of three years before they exit