A save-the-date card, widely shared on social media, pins the Jio World Centre as the venue, with celebrations set to begin on July 12.
A landmark in the heart of Mumbai, the Jio World Centre is a 7.4 hectare business and cultural district owned by the Ambani family's Reliance Industries.
Ambani, 28, is the youngest son of Indian billionaire Mukesh Ambani, one of the world's richest men, while Merchant, 29, is the daughter of industrialist Viren Merchant.
According to the save-the-date card, designed in red and gold, the three-day celebration will begin on July 12 with the “shubh vivaah” or auspicious wedding, with the dress code listed as “Indian traditional”.
This will be followed by “shubh aashirdwad” (the latter word means blessings) on July 13, with guests expected to be dressed in “Indian formal”.
Celebrations will culminate in “mangal utsav” or the wedding reception on July 14 with “Indian chic” being the dress code.
The card is signed by Mukesh and Nita Ambani as well as their children and grandchildren.
The Ambanis are currently on a European cruise, their second prenuptial bash, along with 300 guests, which includes top Bollywood stars. Despite a strict no-phones policy being reportedly in place, videos shared on social media showed Backstreet Boys performing their 1997 hit Everybody (Backstreet's Back) on the cruise liner.
Pop star Rihanna performed at the first pre-wedding bash in Jamnagar, Gujarat, in March. The three-day event was attended by world leaders as well as top businessmen including Bill Gates and Mark Zuckerberg.
Featuring choreographed Bollywood-style stage productions, massive fireworks and multiple themed parties, the pre-wedding event alone is rumoured to have cost more than 12 billion rupees ($144 million), according to India's Financial Express.
Celebrated Indian fashion designer Manish Malhotra, creative director for the event, told The Nationalit was something he'd cherish all his life. “Looking back, we were all like: 'Oh my god, it went so well.'” It was such a memorable experience,” he said.
Ivanka Trump, her husband Jared Kushner and their daughter Arabella. Reuters
Bill Gates and Paula Hurd. Reuters
Actor Shah Rukh Khan, his wife Gauri and their son Abram. Reuters
Actor Ranbir Kapoor and his wife and actor Alia Bhatt. Reuters
Rihanna, third from left, with members of the Ambani family during the first night of pre-wedding celebrations. Reliance Industries / Reuters
The singer performed some of her biggest hits in a rare performance. Reliance Industries / Reuters
Bill Gates and girlfriend Paula Hurd with Anant Ambani and Mukesh Ambani during the pre-wedding celebrations. Reliance / Reuters
Radhika Merchant and Anant Ambani address guests during day one of their three-day pre-wedding celebrations in Jamnagar. All photos: AFP / Reliance unless stated otherwise
Nita Ambani, chairwoman and founder of the Reliance Foundation
Bollywood stars Kareena Kapoor Khan and Saif Ali Khan
India's former cricket captain Mahendra Singh Dhoni with wife Sakshi
Bollywood actors Ajay Devgn, centre, and Akshay Kumar, right
Meta chief Mark Zuckerberg with wife Priscilla Chan
West Indies's former cricket captain Dwayne Bravo, right, and wife Regina Ramjit
From left, Jared Kushner, daughter Arabella and Ivanka Trump posing with billionaire industrialist Mukesh Ambani
Indian businesswoman Natasha Poonawalla
From left, Ivanka Trump, daughter of former US president Donald Trump, and Nita
Akash Ambani, left, with wife Shloka Mehta and Mukesh Ambani, right, with wife Nita
India's spiritual guru and founder of Isha Foundation, Jagadish 'Jaggi' Vasudev, popularly known as Sadhguru
Indian politician Praful Patel with wife Varsha
Malhotra also helped put together the wedding of Anant's sister, Isha Ambani, in 2018. Spread across Udaipur in India, Lake Como in Italy and then at the Ambani home in Mumbai, the wedding was rumoured to have cost more than 7 billion rupees. Beyonce performed a 45-minute show in Udaipur, which also featured a number of costume changes.
Then considered one of the most expensive Indian weddings of all time, Anant and Radhika's wedding celebrations have already dwarfed that even before the main wedding takes place in July.
Anant Ambani and Radhika Merchant at their pre-wedding even in Jamnagar, Gujarat, India, dressed by Manish Malhotra. All photos: Manish Malhotra
Mother of the groom Nita Ambani
Nita worked closely with Malhotra to design the three-day bash in Jamnagar
Akash Ambani, Anant's older brother, dressed in Manish Malhotra
Shloka Mehta Ambani, Akash Ambani's wife
Bride-to-be Merchant in Manish Malhotra
Isha Ambani, older sister of Anant, at one of the themed nights, dressed by Manish Malhotra
Shloka Mehta Ambani in one of her outfits from the three-day event
Shloka in a Manish Malhotra creation
Nita dressed in Manish Malhotra
Anand Piramal, the husband of Isha Ambani
Groom-to-be Anant is the youngest child of Mukesh and Nita Ambani
Nita with daughter Isha Ambani
Shloka in Manish Malhotra
Isha in Manish Malhotra
Isha in one of Malhotra's creations
Nita and Mukesh Ambani perform on stage
World leaders, business tycoons and Bollywood's top stars attended the event
Malhotra says he had five months to put the event together
Malhotra, 57, has a long relationship with the Ambanis
The event was a precursor to the main wedding
Malhotra will also design the main wedding event on July 12
The event featured choreographed Bollywood-style stage productions
There were also fireworks displays and multiple themed parties
The pre-wedding bash alone is rumoured to have cost more than 12 billion rupees ($144m)