Small Business Administration head Linda McMahon will step down to become the chair of the pro-Trump America First organizations, sources familiar with the matter told CNBC on Friday.

McMahon will leave her Cabinet-level role in President Donald Trump's administration on April 12.

"She has been one of our all-time favorites," Trump said of McMahon in remarks to reporters Friday afternoon at Mar-a-Lago, his Palm Beach, Fla., resort.

"She's going to go and help us with a very, very important year and a half that we have coming up," Trump said, adding that "we'll be making a new nomination and appointment in a very short distance."

A spokeswoman for America First did not return CNBC's request for comment. Neither the Small Business Administration nor the White House immediately provided comment to CNBC.

McMahon, 70, and her husband, Vince McMahon, co-founded the company that became World Wrestling Entertainment. They were among then-candidate Trump's biggest fundraisers in his successful 2016 presidential campaign, donating millions to pro-Trump super PACs.

The McMahons gave $6 million to Rebuilding America Now, a super PAC that has reportedly come under investigation by federal prosecutors for possible campaign finance violations.

"While it has truly been the honor of a lifetime to serve our country in this Administration, it is time for me to step down and return to the private sector," McMahon said in a statement. "I am resigning my position at SBA effective April 12. I wish to thank the President and I will continue to be a strong advocate for him and his policies."

McMahon had been nominated to lead the Small Business Administration in December 2016, before Trump had been inaugurated. Her tenure has been a relative island of calm in an administration where the president has publicly broken with several of his Cabinet members, and where top officials have frequently left the White House under a cloud.

Sources told CNBC in November that Trump had favored McMahon as a possible replacement for Commerce Secretary Wilbur Ross. But Ross has remained in the Cabinet role despite Trump's reported comments.

McMahon had twice run for Senate in Connecticut as a Republican in 2010 and 2012, losing to both of the state's current Democratic Sens., Richard Blumenthal and Chris Murphy.

This is developing news. Please check back for updates.