Here are the Top 10 points in this big story:
In his first address to the people after being named Prime Minister, Rishi Sunak said it was the "Greatest privilege of my life...Will work day in and out to deliver".
Congratulating Rishi Sunak, Prime Minister Narendra Modi tweeted, "I look forward to working closely together on global issues, and implementing Roadmap 2030. Special Diwali wishes to the 'living bridge' of UK Indians, as we transform our historic ties into a modern partnership".
Rishi Sunak is the third Prime Minister UK had in seven months. Liz Truss -- who pipped him to the post in the party's internal election and succeeded Boris Johnson -- quit on October 20 after only 45 days in office.
Mr Johnson, who entered the race again last week, cutting short a Caribbean holiday, ended his bid for the post yesterday in a surprise decision. He said he would not be able to lead "a united party in parliament".
The other contender, Penny Mordaunt, failed to secure the numbers and dropped out of the race. Mr Sunak has the support of 180-plus members of the parliament - far above the 100-mark required to bag the top job.
Liz Truss had quit the top post after her plan for a mini-budget -- featuring massive unfunded tax cuts -- spooked markets. "Given the situation, I cannot carry out the mandate for which I was elected," she had told the media.
UK is facing an economically toxic combination of recession and rising interest rates. Critics blame the economic downturn on the Conservative Party and what they call its "series of miscalculations".
The pound rose briefly today as it became clear that Mr Sunak will be the next Prime Minister. "I want to fix our economy, unite our party and deliver for our country," the Indian-origin former chancellor had said earlier.
Rishi Sunak had criticised Liz Truss's tax-cutting agenda during the contest for leadership earlier this year. He said he would cut taxes only after bringing inflation under control. He had also outlined a plan to cut income tax from 20% to 16% by 2029.
Mr Sunak's being named to the UK top post on Diwali has elated many in India, where he is better known through his wife. Akshata Murty is the daughter of Infosys co-founder Narayana Murthy.
Rishi Sunak Makes Apology Calls To Ex-MPs After UK Election Loss Rahul Gandhi's "Victories, Setbacks" Note To Rishi Sunak After Poll Loss After Crushing Poll Defeat, UK's Conservatives Scrambling To Rebuild 150 mg Semen In Kolkata Doctor's Body, Suspect Gang-Rape: Parents To Court 2 French Rafale Jets Collide Mid-Air, Instructor, Pilot Missing "Attempt To Save Accused Instead Of...": Rahul Gandhi On Doctor Rape-Murder Taylor Swift To Return To Stage For Eras Tour After Vienna Attack Plot "140 Crore Indians Worried About Safety Of Hindus In Bangladesh": PM Modi G20 Nations Couldn't Do, India Did, Met Paris Accord Target Before Time: PM Track Latest News Live on NDTV.com and get news updates from India and around the world.