Many Indians, long accustomed to political stagnation, believed him.
But in recent weeks, critics - and even many supporters - have started to accuse him of squandering his powerful mandate in this boisterous country of 1.3 billion people, where such overwhelming election victories are exceedingly rare.
While acknowledging that Narendra Modi only took office in May, they say they see no change, just more of the same.
Despite Narendra Modi's declarations to engage Pakistan - and inviting Prime Minister Nawaz Sharif to his inauguration - ties between the two nations remain stuck where they have been for at least a decade.
The recent national budget announcement - despite promises of urgent reforms - failed to provide new direction to India's listless economy. And Narendra Modi's pledge to clean up the political system has been tainted by the appointment of Amit Shah, a longtime adviser, to a top political post even though he is facing murder charges.
"For a government that promised a new narrative, the adjustment to old ways is striking," Pratap Bhanu Mehta, who heads the Center for Policy Research in New Delhi, wrote in The Indian Express newspaper recently.
The grumbling can be seen on newspaper opinion pages and heard in the bazaars of New Delhi, where Indians from all walks of life shop for food. Staples of the Indian kitchen like potatoes and tomatoes continue to cost well over a dollar per kilogram, exorbitant for many people. Under the campaign slogan of "Better Days Ahead," Modi's party had promised to control food prices, among other things.
"Who can afford to eat tomatoes these days" asked Sunehri Devi, a 70-year-old who says she's learning to cook without the key ingredient in almost every Indian curry. "If I buy the tomatoes I won't be able to buy anything else."
As she filled her shopping bags with potatoes and pumpkin, Devi said the new government has dashed her hopes of a quick fix to the surging living costs.
"These politicians all make big promises before elections," she said. "And now not a squeak out of them."
Some say Modi's government should be given some breathing room.
"You can't start attacking it from day one because it hasn't really done anything worthy of attack," said Ashok Malik, a political analyst and journalist. "But within four or five months I expect more regular criticism to start."
Modi's right-wing Bharatiya Janata Party says the government is only three months old and that addressing India's many complex problems will take time.
"We have had to deal with a lot of problems left behind by the previous government. There are challenges like inflation, and we will tackle them strongly," said Mukhtar Abbas Naqvi, spokesman for the BJP.
"One must remember that this is not a verdict for two or four or six months," he said. "We have a mandate for five years and our work will be judged over five years. We have only just started working."
Still, voters are dismayed by Narendra Modi's initial steps - or lack of them.
During the campaign, he had played up his economic credentials, pointing to the industrial revival of Gujarat state during his time as CM there. He stressed his vision to transform the nation's economy.
But the national budget announced July 10 was widely panned as being little more than an extension of the previous government's populist - and enormously expensive - policies. Modi retained programs subsidizing grains, sugar and fuel, as well as caps on foreign direct investment, which limit fresh capital to fuel business ventures.
Last week, in a speech commemorating India's independence from Britain, he referred to some campaign promises, including accelerating economic reforms, which lifted India's benchmark stock index to a record. But it was mostly a ceremonial speech and didn't spell out more specifics.
And after the grand gesture of inviting Pakistan's Sharif to his inauguration, ties between the two countries remain strained, particularly over the disputed northern territory of Kashmir, which the two nations have gone to war over twice. Modi's first foreign trip was to India's tiny and least controversial neighbor, Bhutan.
"After that big start, inviting Nawaz Sharif to the swearing-in, people are already likening him to Manmohan Singh," Modi's subdued predecessor, said Neerja Chowdhury, a political journalist.
Just this week, a diplomatic spat with Pakistan put the brakes on renewing the peace process over Kashmir. On Monday, India canceled talks with Pakistan after the country's ambassador to India met with Kashmiri separatist leaders. Modi's government had warned the envoy to avoid such a meeting, but analysts said India overreacted by calling off the talks entirely.
"Pakistan has held meetings with separatists before; it is not necessary for India to allow itself to be provoked in this manner," said Neelam Deo, director of Mumbai-based think tank Gateway House.
And given Modi's loud promises to crack down on the corruption and cronyism associated with the Congress-led government, his decision to name Shah head of the Bharatiya Janata Party appears oddly inconsistent.
Accused of ordering the illegal police killing of a small-time criminal and his wife, Shah was arrested and spent three months in jail in 2010. He denies the accusations and has been out on bail while the cases against him make their way through India's painfully slow court system.
The two men go way back. Shah was the main architect of Narendra Modi's electoral victory and the two men have worked closely since the 1980s when they were volunteers with the Rashtriya Swayamsevak Sangh, or the National Volunteers Association, a militant Hindu movement and parent organization of the BJP.
"Amit Shah's elevation also shows that loyalty is above the principles he's been espousing," Chowdhury said.
For all his fiery stump speeches, Narendra Modi has been conspicuously quiet since taking office.
"He's gone into a shell after so much visibility in the last few months. He's already become invisible and inaccessible," Chowdhury added. "If he won't keep the dialogue with the people then it's going to be hard for him to keep their sympathy."