For the first time in nearly 40 years, Congress has moved to establish a new national holiday, this time for Juneteenth, and just in time for Saturday’s 156th anniversary of the day that marks the last African American slaves being freed in Texas in the wake of the Civil War.

The House voted Wednesday night to pass the legislation. It heads next to President Joe Biden’s desk for a signature. When Biden signs it, as he’s expected to at 3:30 p.m. ET Thursday, according to the White House, Juneteenth will officially become a federal holiday — the first since Martin Luther King Jr. Day was signed into law in 1983.

Democratic Rep. Sheila Jackson Lee of Texas, a fierce advocate for the Black community who sponsored the legislation in the House, proudly announced from the podium the “bill is passed” before bringing the gavel down.

One Republican, Rep. Matt Rosendale of Montana, said in a charged statement ahead of the evening vote that he opposed the legislation that was “an effort by the Left to create a day out of whole cloth to celebrate identity politics.” Sen. John Cornyn, R-Texas, a lead sponsor of the Senate bill, called the statement “kooky” in a tweet.

The final vote in the House was 415-14.

Other House Republicans who voted no on the legislation include Reps. Thomas Massie, Scott DesJarlais, Mo Brooks, Andy Biggs, Tom Tiffany, Doug LaMalfa, Tom McClintock, Mike Rogers, Andrew Clyde, Ralph Norman, Chip Roy, Paul Gosar and Ronny Jackson of Texas.

The House vote came after the Senate — in a surprise move Tuesday — passed the measure by unanimous consent following a single Republican senator dropping his opposition.

Republican Sen. Ron Johnson of Wisconsin, who opposed the legislation last year, said in a statement that he would no longer raise his objections on the floor, though, as of last week, the bill already had the support of 60 cosponsors to overcome a filibuster.

“Although I strongly support celebrating Emancipation, I objected to the cost and lack of debate,” Johnson said, referring to his previous stance. “While it still seems strange that having taxpayers provide federal employees paid time off is now required to celebrate the end of slavery, it is clear that there is no appetite in Congress to further discuss the matter.”

Biden will be accompanied for the signing by Vice President Kamala Harris, who was one of the Democrats to introduce the legislation in the Senate last year alongside Cornyn.

Steve Williams, the president of the National Juneteenth Observance Foundation, thanked lawmakers in a press conference on Capitol Hill earlier for, he said, “put(ting) that exclamation mark on the fabulous work.”

“The Juneteenth nation is ecstatic,” he said.

What is Juneteenth?

Juneteenth — also known as Freedom Day, Liberation Day and Emancipation Day — marks the day when federal troops arrived in Galveston, Texas, on June 19, 1865, to ensure that African Americans still enslaved were freed following both the signing of the Emancipation Proclamation and end of the Civil War.

The advance by Union Army Gen. Gordon Granger came 30 months and 19 days after President Abraham Lincoln signed the Emancipation Proclamation on Jan. 1, 1863, which had declared, “all persons held as slaves within any States, or designated part of the State, the people whereof shall be in rebellion against the United States, shall be then, thenceforward, and forever free.”

But with the seven Confederate states operating under their own president, slaves in the South weren’t exactly free to go. It would take another two months after Robert E. Lee surrendered at Appomattox Court House in April 1865 that troops would arrive in Galveston to free the final 250,000 people enslaved there. Most left the area despite a message from Union troops that they could stay and work for their owners as employees.

A few months later, in December 1865, the 13th Amendment to the Constitution was ratified and abolished slavery.

Where is it celebrated?

Like most holidays, Juneteenth is recognized in gatherings across the country, predominantly in the Black community. With the help of social media to spread awareness on a holiday not always taught in school, it has become more mainstream in recent years.

Celebrations can include reflections, parades, food and drink, music — and even advocacy.

For instance, in 2016, Opal Lee of Texas, a now 94-year-old activist, walked from her home in Fort Worth to the nation’s capital in an effort to get Juneteenth named a national holiday.

It was in 1979 that Texas became the first state to officially establish Juneteenth as an official holiday. Now, 49 states and the district separately recognize the day, with South Dakota as the only outlier, despite legislative attempts earlier this year.

Companies including Nike, Twitter, Google and General Motors have also signed on to make Juneteenth a paid company holiday, with several companies adopting the policy last year in the wake of the killing of George Floyd.

What’s next?

The legislation has passed just in time for the holiday Saturday. Biden is scheduled to sign the bill into law Thursday afternoon.

Despite the bipartisan victory, advocates said they are still far from repairing the wounds from American slavery.

Some point to HR 40, which specifically calls for the creation of a commission to study “and consider a national apology and proposal for reparations for the institution of slavery, its subsequent de jure and de facto racial and economic discrimination against African Americans, and the impact of these forces on living African Americans, to make recommendations to the Congress on appropriate remedies, and for other purposes.”

A version has been introduced in every legislative session since 1989, but passed out of a House committee for the first time this year.

“We’re giving America the opportunity for redemption, for repair, for restoration, for also understanding the new America, which is so multicultural,” said lead sponsor, Jackson Lee, in April after it passed.

That legislation is still awaiting a full House vote and is expected to face an uphill battle in the Senate.

Massachusetts Sen. Ed Markey, another lead Democrat to sponsor the legislation making Juneteenth a federal holiday also highlighted in a tweet Wednesday that even with its passage, Republicans still attack critical race theory which would allow students to study the roots of events, such as Juneteenth, in school.

“Even today, as conservatives try to erase history with their attacks on critical race theory and understanding the impacts of systemic racism, we stand here acknowledging the truth. We will make #Juneteenth a federal holiday,” Markey said in the tweet.

Speaking at a press conference earlier Wednesday in front of the Capitol, a group of lawmakers including Jackson Lee and other Democrats supportive of the Juneteenth legislation said there is still work to be done.

“Of course today is not enough, there’s so much more work left to be done, but this is an important day because it is a piece of pavement on that path towards justice,” said Sen. Tina Smith, D-Minn. “This is not a moment for complacency, this is a moment to rededicate ourselves to that work.”

ABC News’ Mariam Khan contributed to this report.