The grim milestone was reached only five days after the US, the world's hardest-hit nation, recorded 400,000 deaths from COVID-19.
The US virus death toll is not more than 417,000 and predicted to surpass 500,000 by February.
The US caseload remains by far the world's highest in absolute terms.
After the first COVID case was reported in the US in January 2020 it took until late April for the figure to pass one million. The overall number of cases has followed an almost exponential curve upwards since then.
Former president Donald Trump came under frequent criticism for perceived inaction in combating the coronavirus.
Xavier Becerra, Biden's secretary of health and human services nominee, likened the COVID-19 trajectory under Trump to a plane about to crash.
"We've got to pull it up and you aren't going to do that overnight, but we'll pull it up -- we have to pull it up," he told CNN.
"Failure is not an option here."
The US has now recorded 25,003,695 million cases, according to the Baltimore-based university's coronavirus tracking website -- though with testing shaky at the start of the pandemic, the real toll is believed to be much higher.
‘COVID battle, a US priority’
Biden is pushing for Congress to approve a $1.9-trillion relief package that would include billions of dollars to boost vaccination rates.
Some US Republicans opposed such a “hefty package” only a month after Congress passed a $900 billion relief measure.
“It seems premature to be considering a package of this size and scope,” said Republican Senator Susan Collins.
White House Principal Deputy Press Secretary Karine Jean-Pierre said, “We can’t wait. Just because Washington has been gridlocked before doesn’t mean it needs to continue to be gridlocked.”
White House Chief of Staff Ron Klain said on Sunday that the Trump administration lagged far behind its target of 20 million Americans inoculated by the end of 2020 and left no plan for how to distribute the vaccine to millions of Americans.