LONDON — Just two months ago, Ireland’s leader, Leo Varadkar, was a spent force in Irish politics: a trailblazing prime minister whose failure to solve Ireland’s housing crisis frustrated voters and whose aloof style left them cold. In a three-way Parliamentary race in February, his party finished last.

Last month, Dr. Varadkar, still in office as a caretaker, reactivated his registration as a medical doctor and said he would spend half a day each week fielding calls from people who believe they have contracted the coronavirus. What many Irish might have once dismissed as a shameless publicity stunt was instead greeted with broad support — a retired doctor doing his bit to help a great national effort.

To the list of politicians whose fortunes have been rescued by the pandemic, add Leo Varadkar’s name.

Ireland has not escaped the scourge of the coronavirus, with 263 deaths, 6,574 confirmed cases, and the expectation is that both numbers will spike in the coming weeks. Its death rate is somewhat lower than Britain’s, while its reported rate of infection is slightly higher.

Yet Dr. Varadkar, 41, is winning praise for his energetic handling of the crisis. He canceled St. Patrick’s Day festivities, oversaw an aggressive early testing program, closed pubs and schools earlier than other European leaders and has spoken to the public about the contagion in honest, humane terms — in other words, like the general practitioner he once was.

“He was at sixes and sevens after the election, but he is perceived as having gotten back on track,” said Pat Leahy, the political editor of The Irish Times. “There is a sense that he showed strong, quick leadership in getting to grips with it.”

He added, “We’re all very familiar with the situation in the U.K.”

In Britain, Prime Minister Boris Johnson’s advisers debated how aggressively to curb the spread of the virus, allowing testing to lag. He was reluctant to order pubs and cafes to close, and his relaxed approach to social distancing came back to haunt him when he contracted the virus himself, ending up in an intensive care unit.

With Mr. Johnson bedridden while Dr. Varadkar counsels patients, the comparisons between these neighbors are as inevitable as they are invidious.

Britain has 13 times the population as Ireland and is far more densely populated, with a capital, London, that has nearly twice as many people as the entire Irish Republic. Its gateway airport, Heathrow, handles 75 million international passengers a year, compared with 31 million for Dublin.

“Some of the difference may be serendipity,” said Dr. Patricia Kearney, an expert in epidemiology at the University College Cork. “We have a relatively small population, and the way we live outside the cities is far less dense than in the U.K. But there was still really decisive action by our political leaders.”

Dr. Varadkar’s performance has not completely escaped criticism. Some people clucked over his decision to keep his annual St. Patrick’s Day date with President Trump in Washington during the early days of the outbreak. While there, he called a dramatic news conference at Blair House, opposite the White House, to announce he was closing Irish schools and banning large gatherings.

Later, the prime minister, or Taoiseach, as he is known in Ireland, was criticized for saying that people might prefer to lose their jobs because they would qualify for a weekly pandemic unemployment payment of 350 euros ($ 380). That played into a familiar critique that Dr. Varadkar, the son of an Indian-born doctor and an Irish nurse, has little empathy for those in economic hardship.

But he compensated for those stumbles with an address on St. Patrick’s Day that was viewed by commentators as one of the most memorable ever delivered by an Irish leader.

“We need to halt the spread of the virus, but we also need to halt the spread of fear,” Dr. Varadkar declared. “Fear is a virus in itself.”

Noting that his partner, Matthew Barrett, as well as his sisters and their husbands are employed in health care, he said: “I am so proud of all of them. Not all superheroes wear capes; some wear scrubs and gowns.”

Dr. Varadkar’s decision to go back to work as a physician was motivated by a desire to help ease the burden on health care workers, his spokesman said. He also issued a plea for emigrant Irish doctors and nurses, and others who had left the field, to return to help with the surge of patients. So far, 60,000 have responded.

The prime minister’s medical career was neither long nor particularly distinguished. He worked as a junior doctor and qualified as a general practitioner in 2010 before leaving to enter politics. His name was removed from Ireland’s medical register in 2013.

To the extent Mr. Varadkar’s training has informed his response to the pandemic, analysts said, it has mainly been in his heeding of expert advice, particularly from Ireland’s chief medical officer, Dr. Tony Holohan. He also has a firsthand grasp of the importance of masks, surgical gloves and gowns.

Last month, Ireland got in early in negotiating a €208 million ($ 226 million) deal with China for this protective gear and scheduled Aer Lingus flights to bring it back. Some of the gowns had been cut for Chinese medics and were too short for Irish doctors. But today Ireland is not suffering from the shortages that afflict other countries. Nor does it have a shortage of ventilators, thanks to a chain of manufacturers.

At the outset of the contagion, Dr. Kearney said, Ireland aggressively tested and traced the contacts of people with symptoms. That quickly stretched its testing capacity, and it was forced to pull back.

As in Britain, there is now a long backlog of people waiting for tests. Still, while Ireland lags top performers like Iceland and Norway, it has tested at more than double the rate of Britain.

Ireland also moved swiftly to impose social distancing, working off an influenza pandemic plan developed 13 years ago, said Dr. Samuel J. McConkey, an infectious disease and tropical medicine specialist at the Royal College of Surgeons in Ireland.

It called off a major rugby match between Ireland and Italy in late February, an unpopular decision at the time. But now, experts said, people are adhering to Ireland’s lockdown better than those in Britain. On Friday, Dr. Varadkar announced the restrictions would stay in place until May 5.

“We’ve all rolled in behind these measures,” Dr. McConkey said. “Even though we’ve had a legacy of shooting at each other over decades, we’re actually quite a socially cohesive society.”

For Dr. Varadkar, the crisis could even give him a role in a new government, something he could scarcely have expected after his defeat. His Fine Gael party is in talks with its archrival Fianna Fail, and the possibility of a unity government is greater than it was before the virus struck, though some find the horse-trading at this time unseemly.

“The prospects for forming that government depend on what happens in the hospitals over the next two to four weeks,” Mr. Leahy said. “Things could switch pretty violently if the outbreak gets bad.”

Anna Joyce contributed reporting from Dublin.