On Saturday, shortly after Pennsylvania was called for Mr Biden, Secretary Clinton tweeted: “The voters have spoken, and they have chosen @JoeBiden and @KamalaHarris to be our next president and vice president.
“It's a history-making ticket, a repudiation of Trump, and a new page for America. Thank you to everyone who helped make this happen. Onward, together.”
Kamala Harris will be the first woman, and woman of colour, to serve as the vice president when she takes office alongside Mr Biden on 20 January.
Sec. Clinton was the Democratic candidate in the 2016 election, when she lost to Donald Trump by 304 to 227 electoral college votes.
On Saturday morning, Mr Biden was declared the winner in Pennsylvania, which pushed him over the 270 electoral college votes needed for the presidency.
The announcement came four days after Tuesday’s election. Mr Trump continues to claim without evidence that the election was being “stolen” from him.
Mr Trump baselessly claimed that there had been widespread voter fraud, after he lost his lead in several states when mail-in-votes were counted.
Mail-in-votes were only counted in multiple states after election day. Mr Trump spent months attempting to delegitimise the practice without citing any evidence for his claims that it would lead to widespread fraud.
Ms Harris’ husband, Doug Emhoff, also congratulated his wife, by captioning a photo of them hugging: “So proud of you. ❤️❤️🇺🇸🇺🇸 .”
Vice president-elect Harris tweeted: “This election is about so much more than @JoeBiden or me. It’s about the soul of America and our willingness to fight for it. We have a lot of work ahead of us. Let’s get started.”
She also shared a short clip of a phone call with Mr Biden, where she said: “We did it. We did it, Joe. You’re gonna be the next President of the United States.”
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