The two-day summit from September 9 will have the most high-profile guest list India has ever welcomed - from United States President Joe Biden to British Prime Minister Rishi Sunak and Saudi Arabia's Mohammed Bin Salman.
However, Chinese President Xi Jinping is likely to skip the meeting, sources in New Delhi and Beijing have said.
Leaders from Australia, Japan, France and Germany are also among those expected to attend, although Russian President Vladimir Putin, who is facing criticism from the West for the war in Ukraine, has said he will be represented by Foreign Minister Sergei Lavrov.
The heads of the United Nations, International Monetary Fund, World Bank, World Trade Organisation and World Health Organisation will also be present.
The event will take place in the sprawling, refurbished Pragati Maidan, a convention and exhibition centre in the middle of one of the most populous cities in the world.
"This is a historic and momentous moment," said Dependra Pathak, a special commissioner of the Delhi Police who is in charge of security arrangements in the city.
Thousands of personnel from other government security services including the home guards and the para-military Border Security Force will be brought in to maintain law and order, he said.
"To contain protests and gatherings, we will have adequate and robust police presence," Pathak said.
While Pathak is in charge of security in the city, the main venue will be guarded by a team under another Delhi Police special commissioner, Ranvir Singh Krishnia.
Although the capital is relatively peaceful, as recently as last month communal tensions flared up in the neighbouring industrial township of Gurugram, where at least seven people were killed.
New Delhi's borders will be closely guarded and access to the city will be regulated during the weekend summit, officials said.
The government is planning a partial shutdown in the city of 20 million during the summit, with schools, government departments and businesses asked to remain closed for three days.
The city will be guarded by almost 130,000 security personnel, including the 80,000-strong Delhi Police, officials said.
A spokesperson for the Indian Air Force told Reuters it would "deploy comprehensive measures for integrated aerospace defence in the Delhi and close-by areas".
The spokesperson said the Indian military, including the air force, the Delhi Police and paramilitary forces would deploy anti-drone systems to prevent any aerial threats.
About 400 firefighters would also be on call.
Security control rooms are being set up at the venue and special security arrangements have been made at key hotels such as the ITC Maurya Hotel, where Biden will stay.
Modi has converted India's year-long presidency of the G20 into a national event, with different meetings of the group being hosted in key parts of the country including far-flung Arunachal Pradesh state and Srinagar city in Kashmir.
Throughout the year, roads, airports, bus stops, parks, railway stations, government offices and government media have been plastered with G20 advertisements.
In New Delhi, new fountains and ornamental plants adorn key traffic roundabouts while life-size cutouts of langurs - a large monkey with a black face - have been put up in several areas to fight the city's monkey menace.
Modi inaugurated a $US300 million ($A464 million) venue in the capital in July to host the summit meeting - a conch shell-shaped building that can seat more than 3000.
The government has also leased 20 bullet-proof limousines at a cost of 180 million Indian rupees ($A3.37 million) to ferry leaders.
Many world leaders travel with their own bodyguards and vehicles.
India has requested countries to be "rational" about the number of cars and personnel they bring, but has not put any restrictions, one government official said.
The official said the US would bring in more than 20 aircraft across a week-long period around the summit.
