Joe Biden vowed to return his country to the Paris climate change accord on his first day in office if he wins the US presidential election.
The United States formally withdrew from the agreement on Wednesday, having helped forge it with other world powers in 2015 to avert the threat of catastrophic climate change.
It was hailed at the time as a victory for multilateralism and the need for every country in the world to work against the ravages of climate change in order to secure the future of the planet.
But a withdrawal was announced by Donald Trump in June 2017, who said the curbs on emissions it introduced were a burden on economic development.
The move had no immediate impact on international efforts to curb global warming, although it further isolated the United States in the world.
Some 189 countries remain committed to the accord.
Biden, who was vice president when the US signed it, said in a tweet late on Wednesday: “Today, the Trump Administration officially left the Paris Climate Agreement. And in exactly 77 days, a Biden Administration will rejoin it.”
The figure referred to the number of days remaining until Wednesday 20 January 2021, when either Biden or Donald Trump will be inaugurated.
Biden had previously criticised Trump's decision to withdraw but had not set an explicit date for an American return under his leadership.
Nigel Purvis, a former US climate negotiator for Bill Clinton and George W Bush, said congressional approval would not be required for such a move and Biden would be able to sign a decree on his first day in office.
The Paris accord aims to keep the increase in average temperatures worldwide "well below" 2 degrees Celsius compared to pre-industrial levels.
It requires countries to set their own voluntary targets for reducing greenhouse gases such as carbon dioxide, and to steadily increase those goals every few years.
The only binding requirement is that nations have to accurately report on their efforts.