It is designed to be a 182m (600ft) high tribute to Sardar Vallabhbhai Patel, a hero in India's independence struggle, in Gujarat state.
The Spring Temple Buddha in China is currently the world's biggest statue at 128 metres.
India's statue has cost 29.9bn rupees (£330m; $430m) and is seen as a pet project of Indian Prime Minister Narendra Modi.
The "Statue of Unity", as it is known, will be inaugurated by the Indian leader on 31 October.
Sardar Patel is revered by many Hindu nationalists
Mr Patel was a deputy to India's prime minister after independence in 1947.
The nationalist was known as the "Iron Man of India" after he persuaded feuding states to unite and become part of the Indian state after independence.
Indian nationalist politicians have used Mr Patel's legacy during election campaigns
Many Hindu nationalists feel his place in history was overlooked in favour of the Nehru dynasty, which came to dominate Indian politics.
While campaigning to becoming India's prime minister in 2013, Mr Modi said "Every Indian regrets Sardar Patel did not become the first prime minister".
Once completed, the bronze-clad statue - which was begun in 2013 - will be nearly twice as tall as New York's Statue of Liberty.
It is hoped the site will become a significant tourist attraction for the country's westernmost state.
The statue is in an isolated part of Gujarat state in the west of India
There will be a viewing gallery some 153m up, near the chest of the statue.
A viewing platform will be located over three-quarters of the way up
The statue is located some 200km (125 miles) from the state's main city, Ahmedabad.
Thousands of workers are constructing the statue in Gujarat
More than 2,500 workers are working to get the statue ready in time, with several hundred migrant labourers from China also contributing to the efforts.