Ukraine's Zelenskyy tells Congress: 'We are united ... the entire free world'

After President Biden's Cabinet walked in, Zelenskyy entered the House chamber to a standing ovation and roaring applause, accompanied by members appointed by House Speaker Nancy Pelosi to escort him.

Zelenskyy, who just one day earlier was visiting soldiers on the front lines of fighting, continued to don his signature army green sweatshirt, green pants and combat boots as he walked up to give his first in-person address outside of Ukraine since Russia's invasion began -- and became the first wartime foreign leader to address Congress since the U.K.'s Winston Churchill during World War II

Zelenskyy stopped to shake lawmakers' hands along the aisle and grabbed hands with Vice President Kamala Harris and Pelosi.

Ahead of Zelenskyy's entrance, Senate Majority Leader Chuck Schumer relayed this message from their closed-door meeting: "He made it clear that without this aid package, the Ukrainians will be in real trouble and could even lose the war."

Presiding over the House chamber, Speaker Nancy Pelosi wore a blue suit with a broach -- the "Order of Olga the Duchess of 3rd Degree," a Ukrainian civil decoration given to her by Zelenskyy when she was in Kyiv, her office said.

Pelosi visited Ukraine in May, marking the first official congressional delegation since Russia invaded.

Here is some early color ahead of Zelenskyy's scheduled 7:30 p.m. remarks to a joint meeting of Congress:

The mood is good inside with members mingling. Early attendees included incoming House Minority Leader Hakeem Jeffries, D-N.Y., and Republican Reps. Matt Gaetz of Florida and Lauren Boebert of Colorado.

Gaetz has been one of the most vocal critics in Congress of future Ukraine funding, vowing a few weeks ago not to support additional money.

Some members are wearing yellow scarves and yellow suit jackets -- an apparent reference to solidarity with Ukraine.

Shortly ahead of Zelenskyy's address, House Speaker Nancy Pelosi welcomed senators to the House chamber for the joint meeting, including Vice President Kamala Harris, president of the Senate.

Wyoming Republican Rep. Liz Cheney was seated on the Democrats' side of the House chamber next to lawmakers she served with on the Jan. 6 committee.

-ABC News' Will Steakin

The big four -- House Speaker Nancy Pelosi, Senate Majority Leader Chuck Schumer, Republican Senate Leader Mitch McConnell and House Republican Leader Kevin McCarthy -- met behind closed doors with Zelenskyy ahead of his address to Congress.

Zelenskyy was spotted walking through Statuary Hall outside the House chamber with Pelosi, Schumer and McConnell, but McCarthy, the likely incoming House speaker, was not with them for that walk.

McCarthy, also needing to win over conservatives to back his bid for speaker, has signaled he could oppose more funding to Ukraine, warning that Republicans will not write a "blank check" for aid when they soon assume the majority.

Some conservative House Republicans have made it clear they would oppose any additional funding even as Congress votes on a must-pass $1.7 trillion government funding bill this week that includes $45 billion in aid to Ukraine.

-ABC News' Katherine Faulders and Lauren Peller