US President Joe Biden canceled the US withdrawal from the World Health Organization and rejoined the 2015 Paris Climate Accord after signing the 17 executive orders in his first hours in office.
"I am committed to working closely with President Biden and other leaders to overcome the climate emergency and recover better from Covid-19," UN Secretary-General Antonio Guterres said in a statement welcoming the actions.
In mid-April last year, as the coronavirus pandemic was spreading across the globe, then-president Donald Trump cut off US funding to the WHO, saying it was "virtually controlled by China."
He then went further, triggering the process to pull the US completely out of the organization. The withdrawal was due to go into effect in July, but Biden's order will cancel it.
The WHO's Executive Board has been meeting virtually this week, and the Biden administration announced that a US delegation, headed by Dr. Anthony Fauci, will participate. The administration has also said it will join Covax, an international alliance dedicated to equitable access to and distribution of the Covid-19 vaccine, especially in poorer countries.
There have been more than 96 million confirmed cases of Covid-19 worldwide and more than 2 million deaths, according to Johns Hopkins University, which tracks the data. About a quarter of the cases and one-fifth of the deaths have been in the United States.
"Supporting the WHO is absolutely critical to the world's efforts for a better coordinated response against Covid-19," UN spokesman Stephane Dujarric said. "Now is the time for unity and for the international community to work together in solidarity to stop this virus and its shattering consequences."
Sitting at his desk in the Oval Office, Biden also signed the instrument to rejoin the Paris Agreement, which Trump withdrew from in 2017, saying it was "in America's economic interest to do so." The former president was a supporter of the fossil fuel industry and often mocked clean renewable forms of energy, such as wind.
Once the instrument is deposited at the United Nations, the US will officially become a party to the accord in 30 days.