Biden added that the coronavirus pandemic "only makes things more urgent" because "it's laid bare just how critical global cooperation is."
He said he would "mobilise the world to fight the defining threats of our time," including nuclear proliferation, terrorism, the climate crisis, mass migration and "the disruptive impacts of new technologies."
Biden also pledged to rejoin the Paris Climate Agreement and the World Health Organisation.
Biden will join forces with his old boss, former President Barack Obama, for a rally in Michigan on Sunday.
The Biden campaign announced the rally but hasn't said where it will be held. Metro Detroit is the Democratic base of the state, with growing non-white populations. Democrats also made gains among suburban white voters in the 2018 Midterms.
President Donald Trump won Michigan by just under 11,000 votes four years ago, making it his closest margin of victory in any state. He won the state through key gains across southwest Michigan in communities where Obama won or lost narrowly. Democratic support in and around Detroit also fell off from 2012 levels when Obama was re-elected.
Biden also said today that he is "not running on the false promises of being able to end this pandemic by flipping a switch" but would prioritise science.
The Democratic presidential nominee tried to keep the focus on healthcare, arguing that a Supreme Court conservative majority stretched to 6-3 by newly confirmed Justice Amy Coney Barrett could dismantle the Obama Administration's signature health law and leave millions of Americans with pre-existing conditions devoid of insurance coverage.
Biden kept most of his focus on the virus, saying Trump's handling of the pandemic was an "insult" to its victims, especially as cases rise dramatically around the country.
"Even if I win, it's going to take a lot of hard work to end this pandemic," Biden said during a speech in Wilmington, Delaware, where he lives.
"I'm not running on the false promises of being able to end this pandemic by flipping a switch. But I do promise this: We will start on day one doing the right things."
Biden was briefed virtually by former Surgeon-General Vivek Murthy, Centre for Science in the Public Interest director Dr David Kessler, New York University medical school assistant professor Dr Celine Grounder and Yale University associate professor of medicine Dr Marcella Nunez-Smith.
- AP
