Biden moved into the White House in January 2021 as the oldest-ever U.S. president.
"Every generation has a moment where they have had to stand up for democracy.
"To stand up for their fundamental freedoms. I believe this is ours," Biden tweeted.
"That's why I'm running for reelection as president of the United States. Join us. Let's finish the job."
The tweet came with a three-minute video clip launching his campaign for re-election in 2024.
Biden won the 2020 presidential election against then-Republican incumbent, Donald Trump.
Biden has been in office since January 2021 and moved into the White House as the oldest president ever.
Biden will be 81 years old at the time of the election in about one year and a half. At the end of a possible second term, he would be 86.
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