Joseph Robinette Biden Jr has been sworn in as the 46th president of the United States, promising to marshal a spirit of national unity to guide the country through one of the most perilous chapters in American history.

Speaking under a bright winter sky, as snow flurries melted and the clouds parted, Biden declared “democracy has prevailed” during a ceremony that honored the ritual transfer of power at the US Capitol, where exactly two weeks ago a swarm of supporters loyal to his predecessor stormed the building in a violent and futile last stand to overturn the results of the election.

“This is America’s day,” Biden said, gazing across the sprawl of the capital city’s national monuments, now guarded by a military garrison unprecedented in modern times and devoid of spectators as a result of the coronavirus pandemic. “This is democracy’s day.”

Millions of Americans watched from home as the Chief Justice John Roberts administered the 35-word oath of office to Biden, moments before noon, when he formally inherited the powers of the presidency. Everyone in attendance, including Biden, wore masks and guests sat apart in the audience.

“Few people in our nation’s history have been more challenged or found a time more challenging or difficult than the time we’re in now,” he said, promising to dedicate his “whole soul” to rebuilding a country ravaged by disease, economic turmoil, racial inequality and political division.

Donald Trump, who never formally conceded his defeat, left the White House on Wednesday morning and was not in attendance, a final display of irreverence for the traditions and norms that have long shaped the presidency. Mike Pence, the outgoing vice-president, was there, joined by the Clintons, the Bushes and the Obamas.

The Biden era dawned in what the president called a “winter of peril and significant possibilities”. He vowed to move forward with the “speed and urgency” required to meet the moment.

That work began just hours after his inauguration. From the Oval Office, Biden signed 17 executive orders and directives, moving swiftly to dismantle the most controversial pieces of his predecessor’s legacy.

“There’s no time to start like today,” Biden said, as he signed the actions. Among them were actions to rejoin the Paris climate accords, terminate the effort to leave the World Health Organization, repeal a travel ban on several predominantly Muslim countries, revoke the permit for the Keystone XL pipeline and extend a pause on student loan payments and a federal moratorium on evictions and foreclosures.

He also imposed a national mandate requiring mask-wearing in federal buildings and sent a sweeping immigration bill to Congress that would create an eight-year path to citizenship for millions of immigrants living in the country illegally.

Waiting for the new president when he arrived in the Oval Office was a note from Trump, one tradition the former leader chose to oblige. Biden declined to divulge its content, telling reporters only that his predecessor left “a very generous letter”.

Kamala Harris, meanwhile, returned to Capitol Hill to swear in the newly elected Democratic senators from Georgia, Jon Ossoff and Raphael Warnock, as well as Alex Padilla, who will replace Harris as a senator from California. Their arrival in the chamber shifted the balance of power, giving Democrats the thinnest possible majority with the vice-president, in her role as president of the Senate, serving as the tie-breaking vote.

Later in the afternoon came another scene that had been a staple during previous presidencies but had remained elusive in the Trump years: a calm, substantial White House press briefing. “When the president asked me to serve in this role, we talked about the importance of bringing truth and transparency back to the briefing room,” the White House press secretary, Jen Psaki, told reporters, while pledging to bring transparency to her role.

Fear and anxiety surrounded the lead-up to Biden’s inauguration. The threat of more violence resulted in the deployment of nearly 25,000 national guard troops, transforming the shining city upon a hill into a military fortress.

The pandemic had already greatly reshaped the inaugural events and ceremony, which typically draws hundreds of thousands of spectators to the National Mall. Much of the area was closed. Instead, flags from the states and territories represented those who the inaugural committee had urged to stay away, out of concern that large crowds would spread the coronavirus, which has now killed more than 400,000 Americans.

Part of Biden’s legacy was secured even before he placed his hand atop a large, 19th-century Bible, a family heirloom accented with a Celtic cross and held by his wife, Jill Biden. Biden, the vice-president to the nation’s first Black president, elevated Harris as America’s first female, first Black and first Asian American vice-president.

“Don’t tell me things can’t change,” Biden said, marking explicitly the history of Harris’s ascension.

The ceremony was enlivened by musical performances. Lady Gaga gave a towering rendition of the national anthem, Jennifer Lopez arrestingly mixed patriotic paeans with the pledge of allegiance in Spanish – “indivisible, con libertad y justicia para todos” – and Garth Brooks asked Americans to join him in singing Amazing Grace.

The celebrations continued into the night. On Wednesday evening, Celebrating America kicked off, a national TV special hosted by Tom Hanks that featured musical performances by Justin Timberlake, Foo Fighters, Demi Lovato, Jon Bon Jovi, John Legend and Bruce Springsteen.

The event, which culminated in an enormous fireworks display over Washington DC, also featured a joint appearance from three former presidents – Barack Obama, George W Bush and Bill Clinton – who urged Americans to come together.

“Obviously there was a personal element to see my former vice-president become the 46th president. To see Kamala Harris as our first woman vice-president,” Obama said. “But more broadly, I think inaugurations signal a tradition of a peaceful transfer of power that is more than two centuries old.”

“I think if Americans would love their neighbor like they like to be loved themselves, a lot of the division in our society would end,” Bush said.

“Everybody needs to get off their high horse and reach out to their friends and neighbors,” Clinton added.

Biden’s inauguration brings to a close one of the most volatile transitions in modern memory, an interregnum that tested the fragility of America’s commitment to an orderly and peaceful transition of power. For weeks after his defeat, Trump whipped up loyalists with baseless allegations of a stolen election.

His claims were dismissed by dozens of courts, security experts, Republican election officials and his then attorney general. But Trump refused to accept his political fate, a decision that culminated two weeks ago in the assault on the US Capitol, where rioters attempted to stop Congress from certifying Biden’s win.

Biden said the events of the past few weeks offered “painful lesson” about the power of words and the threat of conspiracy.

“There is truth and there are lies,” he said, reminding the nation’s political leaders, many of whom were arrayed onstage behind him, that it was their duty to “defend the truth and defeat the lies”.

As Biden spoke, Trump was nearly 1,000 miles away, at his south Florida resort in Mar-a-Lago, where he concluded his historically unpopular presidency and now awaits his second impeachment trial. Earlier on Wednesday, he held a farewell event for families and supporters. In his final hours as commander-in-chief, he boasted that the last four years had been “amazing by any standard” and promised he would “be back in some form”.

Biden never mentioned his predecessor by name but struck a stark contrast in tone and tenor. During his remarks, he paused to observe a moment of silence to remember those who had died from the virus, acknowledging the pandemic’s grim toll in way Trump never did.

Whereas Trump four years ago conjured dark visions of “American carnage”, Biden described a nation capable of overcoming daunting odds and seemingly incontrovertible divisions. He appealed for unity, a dominant theme of his presidential campaign, while recognizing that the plea might sound like “foolish fantasy” in an age governed by tribalism and partisan passions.

“We must end this uncivil war that pits red against blue, rural versus urban, conservative versus liberal,” he said.

Nearly half a century after he was sworn in as one of the nation’s youngest senators, he became the oldest president to take the oath of office, at 78.

A veteran of Washington first elected to the Senate in 1972, where he served until becoming vice-president under Barack Obama in 2009, Biden enters the White House with one of the deepest résumés in American political history, experience he will rely as he faces what he called “this time of testing”.

Loss and recovery have marked his long career in public service. His first wife and his daughter were killed in a car accident days after his election to the Senate. In 2015, he buried his eldest son, Beau, who died of brain cancer.

Biden’s rise to the presidency, the realization of a life’s dream, was paved with false starts and bad timing. A plagiarism scandal plagued his first run. Outshone by the history-making candidacy of his Democratic opponents in 2008, Hillary Clinton and Barack Obama, Biden bowed out before the Iowa caucuses. Then, in 2015, still mourning the loss of his son, Biden opted not to run.

But Trump’s presidency tormented him. Trump’s failure to forcefully condemn the white supremacist violence in Charlottesville, Virginia, in 2017 was Biden’s motivation for launching a third presidential bid. Biden presented himself as a rebuke to Trump – an empathetic figure shaped by personal tragedy who believed he had something to offer the country at a moment of national tragedy.

“We will be judged, you and I, by how we resolve these cascading crises of our era,” Biden said in his address. “Will we rise to the occasion, is the question. Will we master this rare and difficult hour? Will we meet our obligations and pass along a new and better world to our children? I believe we must.”

Maanvi Singh contributed reporting