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Rep. Mark Meadows officially resigned from Congress on Monday, more than three weeks after he was chosen to be President Donald Trump's new chief of staff.

Trump tapped Meadows, R-N.C., who announced in December that he would not seek re-election in 2020, for his new post on March 6.

Mark Meadows resigned from Congress today effective 5:00pm. Below is the letter notifying Speaker Pelosi. First day as White House Chief of Staff tomorrow. pic.twitter.com/1IUCO48AWC — Ben Williamson (@_WilliamsonBen) March 30, 2020

The resignation was effective at 5 p.m. Monday, and he will start his new role Tuesday, his spokesman said.

"Serving the people of North Carolina's eleventh congressional district for these last seven years has been the honor of my life," Meadows wrote in a resignation letter. "I will forever be grateful for the opportunity."

Meadows replaces Mick Mulvaney, who, in an acting capacity, was the president's third chief of staff. Reince Priebus and John Kelly previously served in the role.

Trump has said Mulvaney will become the U.S. special envoy for Northern Ireland.

Meadows, who is considered one of Trump's staunchest congressional allies, was a founding member of the House Freedom Caucus.