Joe Biden, a fixture in US politics for a half century as a senator and vice president, completed a long climb to the political summit that included two previous failed presidential bids by defeating President Donald Trump.
When he enters the White House on 20 January, Biden, at the age of 78, will be the oldest person ever to assume the office.
The Democrat from Delaware played up his political experience during a bitter and divisive campaign, casting himself as a tested leader capable of healing a nation battered by the coronavirus pandemic and providing steadiness after the turbulence of Trump's presidency.
"With age comes a little bit of wisdom," he said before the polls closed on Tuesday.
Edison Research and the major US television networks on Saturday projected Biden's victory over the Republican Trump. Trump has escalated his unsubstantiated attacks on the voting process in recent days, falsely claiming the election was being "stolen" from him.
Trump derided Biden as "Sleepy Joe" during the campaign and said his mental capacity was "shot". The president's allies sought to portray Biden as senile. Trump, 74, was the oldest person to assume the presidency when he was sworn in at age 70 in 2017.
Biden unsuccessfully sought the Democratic presidential nomination in 1988 and 2008 before finally securing his party's blessing this year with strong support among Black voters.
Accepting the nomination in August, he stressed compassion and decency, seeking to draw a contrast with the brash and pugnacious Trump.
"I'll be an ally of the light," Biden said, "not the darkness."
He has brought to his political career a mix of blue-collar credentials, foreign policy experience and a compelling life story marked by family tragedy - the loss of his first wife and a daughter in a car crash, and a son to cancer.
Biden arrived in Washington as a young upstart. He was elected in 1972 at age 29 to the US Senate from Delaware and remained there for 36 years before serving from 2009 to 2017 as vice president under Barack Obama, the country's first Black president.
Biden opted not to run for president in 2016, only to watch Trump defeat Democrat Hillary Clinton. When Biden announced his 2020 candidacy in April 2019, he took aim at Trump.
"We are in the battle for the soul of this nation," he said, adding that, if re-elected, Trump would "forever and fundamentally alter the character of this nation - who we are - and I cannot stand by and watch that happen."
Biden selected Senator Kamala Harris - whose father immigrated from Jamaica and whose mother immigrated from India - as his running mate, making her the first Black woman and first person of Asian descent on a major-party US ticket. At 56, Harris is a generation younger than Biden.
Trump sought to turn Biden's experience into a liability, denouncing him as a career politician and saying Biden would become a puppet of the Democratic Party's "radical left."
The coronavirus pandemic was front and center in the presidential race. Biden accused Trump of surrendering in the face of the public health crisis, saying the president panicked and tried to wish away the virus rather than do the hard work needed to get it under control, leaving the economy in shambles and millions of people jobless.
Trump, who was hospitalized for three days after contracting COVID-19, mocked Biden for regularly wearing a face mask to guard against the pathogen's spread.
An effort by Trump to dig up dirt on Biden resulted in the president's impeachment in the Democratic-controlled US House of Representatives in December 2019. The two articles of impeachment - abuse of power and obstruction of Congress - stemmed from Trump's request that Ukraine investigate Biden and his son Hunter on unsubstantiated corruption allegations.
In February, the Senate, controlled by Trump's fellow Republicans, acquitted him of the charges after refusing to call any witnesses.
US intelligence agencies and the FBI director this year concluded that Russia, after interfering in the 2016 election to harm Trump's opponent Clinton, was engaging in a campaign to denigrate Biden and boost Trump's re-election chances while promoting discord in the United States.
Biden's previous two presidential runs did not go well. He dropped out of the 1988 race after allegations that he had plagiarized some speech lines from British Labour Party leader Neil Kinnock. In 2008, Biden won little support and withdrew, only to be selected later as Obama's running mate.
Under Obama, Biden served as a troubleshooter on matters of war and foreign affairs and on domestic issues such as gun control and fiscal policy.
Obama did not always heed Biden's advice. Obama gave the go-ahead for the 2011 raid in Pakistan that killed al Qaeda leader Osama bin Laden despite Biden's warning that it was too risky.
Biden speaks openly about his family's tragedies including the 1972 car crash that killed his first wife, Neilia, and their 13-month-old daughter, Naomi, weeks after his election to the Senate.
He almost abandoned his political career to care for his two young sons who survived the accident but stayed on, commuting by train from Delaware to Washington to avoid uprooting them.
In 2015, his son Joseph "Beau" Biden III, an Iraq war veteran who had served as Delaware's attorney general, died from brain cancer at age 46. Biden's son Hunter struggled with drug issues as an adult.
Biden himself had a health scare in 1988 when he suffered two brain aneurysms.
Biden was born in the blue-collar city of Scranton, Pennsylvania, the eldest of four siblings. His family later moved to Delaware. He overcame stuttering as a boy by reciting passages of poetry to a mirror.
He was practically a political novice - having served two years on a county board in Delaware - when in 1972 he became the fifth-youngest elected senator in US history.
Despite years of partisan hostilities in Washington, Biden remained a believer in bipartisanship. During his time in the Senate, he was known for his close working relationships with some of his Republican colleagues. A number of disaffected Republicans, including former government officials and former lawmakers alarmed at Trump's presidency, endorsed Biden's bid for the White House.
Biden advocated for America's role as a leader on the world stage at a time when Trump was abandoning international agreements and alienating longtime foreign allies.
While in the Senate, he built up a specialty in foreign affairs and at one time headed the Foreign Relations Committee. He voted in favor of authorizing the 2003 Iraq invasion before becoming a critic of Republican President George W. Bush's handling of the war.