As is traditional, the new President and his Vice President, Kamala Harris, were sworn in on the National Mall in Washington, DC at 12PM local time.
Unlike in the past, however, due to coronavirus safety concerns, members of the public were not allowed to attend.
Other celebrities were excited to watch events unfold from the comfort of their homes, and many shared their feelings on social media.
Keep reading to see all the best celebrity reactions to Joe Biden becoming president…
WATCH: Joe and Jill Biden walk out on inauguration day
"THIS is everything," the Friends star wrote as she shared a clip from Kamala Harris' inauguration to her Instagram Stories.
Before the ceremony, the actress had posted a photo of herself with the new First Lady, Dr Jill Biden.
The former First Lady shared a picture from her husband's inauguration to Instagram and wrote: "Joe Biden and Kamala Harris are the kind of leaders our nation deserves—decent, hardworking people who reflect the best of our values."
Former President Obama shared a sweet photo to Twitter that showed him with his former Vice President and close friend.
Taken from behind, the snapshot showed the two men walking out of the Oval Office with their arms around each other's backs.
He captioned it: "Congratulations to my friend, President @JoeBiden! This is your time."
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The model and author was "reporting" live from her windowsill in D.C, wearing a crisp white bathrobe.
She panned her phone to show her husband John Legend sitting on the carpet floor, and then back to her TV, which showed Joe Biden and Dr Jill Biden.
In the evening, John is set to perform as part of a TV concert to celebrate the event.
So You Think You Can Dance? host Cat Deeley shared a sweet series of videos to her Instagram page where she talked to one of her sons, who was off-screen, about seeing photos on TV of the new President and Vice President.
"Why was it so exciting that one of the pictures was a lady?" she asked.
"Because they've never had a lady," came the response. "Yes!" the presenter said as she beamed at the camera.
The actress broke her silence for the first time since news of the Sex and the City reboot was announced, which she will not star in.
Kim echoed the sentiments of singer Garth Brooks, who performed Amazing Grace at the ceremony.
"Amazing Grace, indeed," she tweeted.
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The Desperate Housewives star shared a photo of herself with the new President to Instagram.
She captioned it: "Today, we make history! Today, we celebrate leaders like President @joebiden and our first Madam Vice President, @kamalaharris. Today is only the beginning."
The Cougar Town actress shared a snap of herself smiling as she posed with her TV on which a close-up of President Biden could be seen.
She captioned the photo: "It’s a new day!"
The star shared a photo to Instagram of her young daughter Katharine wearing pyjamas and watching the inauguration on TV at home.
The Office actress and writer also posted a heart-melting story about the occasion.
She wrote: "I was at work, but apparently she said: 'Is that mommy? It looks like mommy.'
Best compliment I ever got! It matters. Happy Inauguration everyone."