President Trump made a surprise announcement on Friday night that Rep. Mark Meadows, R-N.C., would become his new White House chief of staff, replacing acting chief of staff Mick Mulvaney.

"I am pleased to announce that Congressman Mark Meadows will become White House Chief of Staff. I have long known and worked with Mark, and the relationship is a very good one," Trump tweeted.

Meadows has become one of Trump's most loyal defenders on Capitol Hill, particularly during the monthslong impeachment battle that ultimately ended with an acquittal in February.

MARK MEADOWS TO LEAVE CONGRESS AT END OF TERM

Mulvaney became the acting White House chief of staff in January 2019, replacing Gen. John Kelly. Mulvaney was also serving as the Office of Management and Budget (OMB) director.

Trump also announced that Mulvaney would become the U.S. special envoy for Northern Ireland.

"I want to thank Acting Chief Mick Mulvaney for having served the Administration so well. He will become the United States Special Envoy for Northern Ireland. Thank you!" Trump said in a second tweet.

In a statement, Meadows said it was an "honor" to selected by President Trump.

"This President and his administration have a long list of incredible victories they've delivered to the country during this first term, with the best yet to come -- and I look forward to helping build on that success and staying in the fight for the forgotten men and women of America," he said.

Meadows said Mulvaney did a "great job," and he also thanked his constituents in western North Carolina.

"In particular, I want to recognize my friend Mick Mulvaney. Mick is smart, principled, and as tough a fighter you'll find in Washington, D.C. He did a great job leading the President's team through a tremendous period of accomplishment over the last year-plus," the lawmaker said.

"Lastly, I want to thank the people of western North Carolina," he added. "Serving you in Congress has been the honor of my life. It may be in a different role, but I'll continue working every day to deliver results for you -- and main street Americans all over the country -- in the months and years to come."

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Meadows, 60, had announced in December that he planned to leave Congress at the end of his current term. He has represented North Carolina's 11th Congressional District since 2013. He also chaired the House Freedom Caucus from 2017 until earlier this year, when he was succeeded by Rep. Andy Biggs, R-Ariz.

A source familiar with the situation told Fox News that Mulvaney is expected to resign from OMB. Russ Vought is widely viewed as the nominee to be confirmed by the Senate as his successor at OMB.

Fox News' Matt Leach contributed to this report.