"The voters have spoken, and they have chosen @JoeBiden and @KamalaHarris to be our next president and vice president," Clinton wrote. "It's a history-making ticket, a repudiation of Trump, and a new page for America."
She continued: "Thank you to everyone who helped make this happen. Onward, together."
The victory will make Biden the oldest president ever sworn into office, andthe first woman and person of color to serve in the office.
Clinton, the first female presidential candidate nominated by a major party, lost to Mr. Trump in 2016 with a margin of 227 Electoral College votes to 304. She carried the popular vote by nearly 3 million votes.
CBS News called Biden's win after it was projected he would carry the state of Pennsylvania, netting him a total of at least 273 electoral votes, with several states still to be determined. Mr. Trump carried Pennsylvania in 2016.
Clinton had been a vocal critic of Mr. Trump's throughout his presidency, including his dealings with Ukraine that became the subject of his impeachment hearings.
The Trump campaign released a statement after multiple media outlets projected a Biden win, accusing the president-elect of "rushing to falsely pose as the winner," while also vowing to challenge the vote counts in court.
Biden released his own statement as well, saying he was "honored and humbled" to have won the vote, and called for Americans to "put the anger and the harsh rhetoric behind us and come together as a nation."
The 2020 election saw a r, also shattering records for early votes cast, a majority of which went to Biden.