Evan Vucci/AP/Shutterstock Joe Biden
The June 19 holiday commemorates the day when the last enslaved Black Americans learned they were free, following the Emancipation Proclamation two years earlier in 1863.
After signing the Juneteenth National Independence Day Act into law Thursday, Biden, 78, issued a proclamation Friday morning calling the new federal holiday "a day of profound weight and power."
On Thursday, he and Vice President Kamala Harris delivered remarks in the East Room of the White House after making Juneteenth the country's 12th federal holiday.
"Throughout history, Juneteenth has been known as many things: Freedom Day, Liberation Day, Emancipation Day," Harris, 56, said. "And today, a national holiday."
Biden called the historic moment one of his "greatest honors."
"I have to say to you, I have only been president for several months, but I think this will go down, for me, as one of the greatest honors I will have as president - not because I did it, you did it, Democrats and Republicans," the president said. "It's an enormous, enormous honor."
JIM WATSON/AFP via Getty Joe Biden (left), Kamala Harris
The measure marks the creation of the first new U.S. national holiday since Martin Luther King Day in 1983, Biden said.
Noting the overwhelming bipartisan support of the measure, Biden said: "I hope this is the beginning of a change in how we deal with one another."
The president also used the remarks to introduce Opal Lee, a 94-year-old activist whose childhood home was torched by a white mob. She has spent years marching to make Juneteeth a national holiday.
Calls to make Juneteenth an official holiday have increased over the last year in large part due to a renewed focus on racial injustice in the country. Several states, including Washington and Oregon, had earlier passed bills declaring the date a state holiday.
The Senate unanimously passed the measure to make Juneteenth a federal holiday on Wednesday, followed by the House in a 415-14 vote, before it headed to the Oval Office for Biden's signature.
The White House event had celebrity as well, with R&B superstar Usher in attendance for the historic bill signing.
Oliver Contreras/UPI/Shutterstock Usher
June 19 marks the date that news of the Confederate surrender reached the last enslaved Black people, when Union soldiers brought the news of freedom to Galveston, Texas, in 1865 some two and a half years after the Emancipation Proclamation legally freed slaves in the Southern states.
Listen below to our daily podcast PEOPLE Every Day for more on Juneteenth becoming a federal holiday.
On that day, Maj. Gen. Gordon Granger issued General Order No. 3, announcing that, in accordance with the Emancipation Proclamation, "all slaves are free."
Evan Vucci/AP/Shutterstock Kamala Harris (left), Joe Biden
As Harris explained, the freedom granted that day was significant in part because of how long it took to make official.
"Yes, on that day the enslaved people of Galveston, Texas learned that they were free," she said, "but in fact two-and-half years earlier the Emancipation Proclamation ended slavery in the south."
Harris added: "For more than two years, the enslaved people of Texas were kept in servitude ... and then on that summer day, 156 years ago, the enslaved people of Texas learned the news. They learned that they were free. And they claimed their freedom."
"It was indeed an important day," the vice president said.