"Warmest congratulations Rishi Sunak! As you become UK PM, I look forward to working closely together on global issues, and implementing Roadmap 2030," Modi said on Twitter.
Modi also congratulated Indians in the UK on the Diwali holiday, noting that "we transform our historic ties into a modern partnership."
Earlier in the day, the 42-year-old former finance minister Sunak became the head of the ruling Conservative Party, and as such, the country's youngest next prime minister since 1812 and the first prime minister of Indian origin. Sunak became the only candidate to run for the post after House of Commons' leader Penny Mordaunt withdrew her candidacy.
Sunak will become the third UK prime minister to hold the office this year. On October 20, Liz Truss announced her resignation as UK prime minister, less than two months after her appointment as Boris Johnson's successor, becoming the shortest-serving head of government in UK history.