The UK's first prime minister of colour, who is also an observant Hindu, believes the landmark says something important about the state of diversity in Britain, according to an interview published on Saturday.
The 42-year-old Sunak also revealed that he refused to step aside for ex-PM Boris Johnson in last month's leadership battle, convinced his track record as finance minister meant he was the right person to lead the country through its cost-of-living crisis.
Sunak won the race to replace Liz Truss as premier and leader of the Conservative Party on October 24, the same day Hindus marked Diwali, the festival of lights.
The new premier's first formal event in Downing Street was a Diwali reception.
"It was obviously marvellous. It meant a lot of things to a lot of people," said Sunak, who as Johnson's finance minister would lay out traditional Diwali decorations on the doorstep of his official residence at 11 Downing Street.
Sunak's grandparents hailed from Punjab in northern India and emigrated to Britain from eastern Africa in the 1960s.
"As chancellor I was able to light my Diwali Diyas (lamps) on the steps of Downing Street. It said something wonderful about our country that that was possible, but also that it wasn't a big deal.
"It was in a sense gosh, this is great, but also that's just Britain," he told The Times newspaper in his first major interview since taking office.
"Hopefully it's a source of collective pride across the country," he added.
- 'Best person' for job -
Sunak said he never considered dropping out of the leadership contest to make way for Johnson or a "joint ticket" with his former boss.
Johnson had mulled a comeback attempt but aborted the bid after he failed to persuade Sunak to share power.
"I was very clear with him about the fact I had strong support from colleagues in parliament and I thought I was the best person to do the job," he said.
Sunak avoided direct criticism of his short-lived predecessor Truss, whose disastrous economic policies he has described as "mistakes" it is his job to "fix".
Truss's botched tax-cutting October budget rocked markets, spiked borrowing costs and tanked the pound.
With Britons facing a winter of rising food, energy and housing costs, Sunak has attempted to bring calm to markets by hinting at tax rises in a fresh budget on November 17.
But he warned of "difficult decisions to come", while pledging measures aimed at bringing down inflation "compassionately and with fairness".