In a tweet
she said "inspiring words from President-elect Joe Biden".
"Healing skills are at a premium as new President works to govern for all & unify nation. Calls for demonisation to end here & now & to put away harsh rhetoric" she wrote.
Harris took the stage first where she paid tribute to the late congressman John Lewis, who said: "Democracy is not a state, it is an act."
Harris said that meant protecting democracy.
"We the people have the power to build a better future."
She said the "very soul of America was at stake".
"You ushered in a new day for America."
Biden jogged onto the stage and double fist-bumped Harris before removing his mask to address the crowd.
"The people of this nation have spoken. They've delivered us a clear victory, a convincing victory, a victory for we the people."
"Tonight we're seeing all over this nation, indeed across the world, an outpouring of joy ... I am humbled by the trust and confidence you've placed in me."
After the two speeches, they were joined on stage with their families and the event finished with an impressive fireworks display.
CNN commentator Van Jones, who broke down in tears after Biden's win, also commended the new President for his "inclusive" speech.
"Did you notice that @JoeBiden didn't say anything bad about ANYBODY in his speech?" Jones wrote on Twitter.
"This is a new style of leadership. But it's new because it's classic. Because it's timeless. Because it's inclusive."
Basketball superstar Magic Johnson praised Kamala Harris for her speech, calling it a "powerful message to America".
Hillary Clinton, who took on Trump for the presidency in the 2016 election, called today's result "a repudiation of Trump, and a new page for America".
"It's a history-making ticket," she wrote.
"Thank you to everyone who helped make this happen. Onward, together."
Biden and Harris' speeches have drawn emotional reactions across Twitter.
Producer Natasha Chandel said she "broke down".
Comedy director and producer Payman Benz posted a photo of his mother admiring Harris during her speech
