Ukraine’s president, Volodymyr Zelenskiy, will arrive in Washington on Wednesday where he will meet President Joe Biden at the White House and address a joint session of Congress.

The trip – Zelenskiy’s first known foreign visit since Russia invaded Ukraine – will also see the Ukrainian president meet with congressional leadership and national security committee chiefs from the Republican and Democratic parties.

The trip comes as US lawmakers are due to vote on a year-end spending package that includes about $45bn in emergency assistance to Ukraine. The latest tranche of US funding would be the biggest American infusion of assistance yet to Ukraine, above even Biden’s $37bn emergency request.

“The visit will underscore the United States’ steadfast commitment to supporting Ukraine for as long as it takes, including through the provision of economic, humanitarian, and military assistance,” said a White House statement announcing the visit.

President Zelenskiy confirmed in a tweet that he was on his way to Washington and would be speaking before Congress, as well as conducting a number of bilateral meetings.

In a letter inviting Zelenskiy to address the joint meeting of Congress, House Speaker Nancy Pelosi called the fight for Ukraine a fight for democracy itself.

“In the face of Putin’s horrific atrocities, Ukrainian freedom fighters have inspired the world with an iron will and an unbreakable spirit … your courageous, patriotic, indefatigable leadership has rallied not only your people, but the world, to join the frontlines of the fight for freedom”, Pelosi wrote.

In a conference call with reporters on Tuesday, a senior administration official, who did not wish to be named, said Biden and Zelenskiy had discussed a potential visit when they spoke by phone on 11 December and the White House formally extended an invitation last Wednesday. Zelenskiy’s office accepted the invitation last Friday and the visit was confirmed on Sunday.

Biden will first welcome Zelenskiy at the White House for bilateral meetings with the US president’s national security team and cabinet. After a press conference, Zelenskiy will go to Capitol Hill and address a joint session of Congress. He will return home after just a few hours on the ground.

The official said: “We’re looking forward to having President Zelenskiy back at the White House for his second visit but his first visit since the start of Russia’s brutal war against Ukraine. It’s something we’ve wanted to do for some time and tomorrow is actually the 300th day since Russia brutally invaded Ukraine in an all-out assault with the goal of wiping its neighbour off the map and subjecting the Ukrainian people to Russian dominion.”

Biden will announce a new package of nearly $2bn of security assistance including a Patriot missile battery. The US will, in a third country, train Ukrainian forces in how to operate the Patriot system.

Despite some Republicans questioning the price of the war, the official predicted Zelenskiy would receive a strong bipartisan show of support. “This isn’t about sending a message to a particular political party. This is about sending a message to Putin and sending a message to the world that America will be there for Ukraine for as long as it takes.

“President Putin badly miscalculated the beginning of this conflict when he presumed that the Ukrainian people would yield and that Nato would be disunited. He was wrong on both counts. He remains wrong about our staying power and that’s what this visit will demonstrate.”

The senior administration official also denied that Biden will pressure Zelenskiy to seek a diplomatic end to the war. “The president is not coming with a message that is about pushing or prodding or poking Zelenskiy in any way. This is going to be a message of solidarity and support, coordination and alignment and making sure that we are very much putting Ukraine in the best possible position to defend its interests and secure its objectives.”

Biden has said from the start that the US will not send forces to Ukraine to directly fight the Russians. No change to that policy is expected on Wednesday.

The Associated Press contributed to this report