The Conservative Party leader, the first British prime minister of Indian descent, said he was "excited" to be visiting.
He is joined by his wife Akshata Murty, daughter of NR Narayana Murty, founder of Indian IT company Infosys and one of India's richest tech billionaires.
Mr Sunak, 43, was a regular visitor to the country before he became chancellor of the exchequer in 2020.
Speaking on a flight from London to New Delhi, he told reporters: “Of course, it is special. I'll be visiting a country that is very near and dear to me.
“I haven't been back for a few years. I was meant to go, actually, in 2020.
“We take our family typically in February half-term every year, and I got made chancellor right before and I didn't get to go with the rest of my family then, so I haven't been for a little while.”
Mr Sunak said the trip was “obviously special”.
“I saw somewhere that I was referred to as 'India's son-in-law', which I hope was meant affectionately,” he said.
“But look, I'm excited to be back. It is nice to have Akshata with me, as well.”
The MP for Richmond, Yorkshire, was born in Hampshire, southern England, to Indian migrant parents, a pharmacist mother and a GP father.
The Prime Minister has not shied away from talking about his Indian origins and love for cricket.
He has also spoken about his abstinence from beef on religious grounds as a devout Hindu.
“I am thoroughly British, this is my home and my country, but my cultural heritage is Indian,” he said in 2020.
During his time in New Delhi, Mr Sunak is scheduled to visit important Indian cultural and religious sites, with a trip to a Hindu temple planned during his three-day stay.
The UK and India are in discussions over a free trade deal.
Trade between the two nations is worth £36 billion ($44.9 billion) and in 2022 India was the UK’s sixth largest import market for services.
A representative for the Prime Minister described Mr Sunak’s trip to his ancestral homeland as a “historic moment”.
The sentiment echoed a congratulatory message Indian Prime Minister Narendra Modi sent to Mr Sunak after he succeeded Liz Truss last October.
Mr Modi referred to Mr Sunak as the “living bridge of UK Indians” and expressed hope the two could work together to “transform our historic ties into a modern partnership”.
Mr Sunak's entry into office gave rise to renewed hopes of trade pact with India, but a year on no deal is in sight.
The Prime Minister’s spokesman this week said negotiations were progressing well, a view shared by Indian officials.
Remarks made by Home Secretary Suella Braverman last year when she expressed “reservations” about relaxing immigration controls for Indians as part of any agreement were reported to have provoked an angry response from ministers and officials in New Delhi.
UK Foreign Secretary James Cleverly on Friday appeared to play down concerns that any agreement could involve the UK handing out more student visas.
“We've got to understand that trade deals are trade deals, not travel deals,” he told GB News.
“We have already got a very good relationship with India when it comes to students.
“Student numbers from India are up, but also visa applications in our existing visa system is up.
“India is a growing economy, it is increasingly going to be important economically, politically, diplomatically, in years to come and the fact that we've already got a good relationship … is fantastic.
“We're looking to build on that. And India is seeking to do a trade deal with us and us seek to do a trade deal with them for trade purposes, rather than anything else and the advantages of trade are self-evident.”
Mr Cleverly dismissed criticism of the slow progress towards a UK-India trade pact.
He emphasised the importance of ensuring the agreement right.
“Our trade negotiations with India have actually progressed much quicker than other trade negotiations, including the EU’s trade negotiations with India,” he told Sky News.
“We’ve always said we want to get the right trade deal with India because it is an incredibly important partner.”
Asked whether a much-anticipated agreement could happen before the next general election, expected next year, Mr Cleverly said: “Of course we want one and we seek to resolve it as quickly as possible as long as it is a properly mutually beneficial trade deal.”
He said that the government did not want to “rush it through”.
Climate will be a key focus of discussions at the G20 summit, Mr Cleverly said.
Mr Sunak will bring the topic up at the meeting with allies and “demonstrate how you can have economic growth and reduce carbon emissions” at the same time, the minister said.