The most contentious battle for House speaker in more than 160 years has officially come to an end.

Days after being called a "squatter" by some members of his own party -- McCarthy now has his name across the House speaker's office.

"I will work with anyone and everyone who shares our passion to deliver a better future for our nation,” McCarthy pledged as he received the gavel early Saturday morning. “As a Congress, we can only operate if we cooperate. My door will be open. I'd like you to come by."

-ABC News' Rachel Scott

"I may not know all of you, some of you are new," McCarthy said as he wrapped up his remarks. "But I hope one thing is clear after this week: I never give up."

"I make this promise, I'll never give up on you the American people," he added.

McCarthy then took his oath of office and is now the 55th speaker of the House of Representatives.

"That was easy, huh?" McCarthy joked as he received the speaker's gavel from Democratic Rep. Hakeem Jeffries. "I never thought we'd get up here."

As he listed his priorities for the 118th Congress, McCarthy said it was time for the Republican majority to be a check and provide a balance to President Joe Biden's policies.

"And now the hard work begins," he said. "What we do here today, next week, next month, next year will set the tone for everything that follows."

At approximately 1:15 a.m. Saturday, McCarthy was handed the speaker's gavel from Democratic caucus leader Hakeem Jeffries.

But before Jeffries turned it over to McCarthy, he ran through a list of Democratic accomplishments over the past two years and gave a final nod to former House Speaker Nancy Pelosi.

"Pelosi will go down in history as the greatest speaker of all time," Jeffries said.

Jeffries said this is a moment of "transition" for Congress, from a "year of accomplishment to a year of ambiguity."

"But we do extend our hand of partnership to you," he said.