Wilson's name had come up as a potential replacement for Mattis, who quit in December because of differences over Trump's policies on Syria and other issues.

Wilson reportedly raised concerns last year about Trump's desire for a separate space force, but more recently embraced the Pentagon's plan to set up a space service under the Air Force.

"Today I informed the President I will resign as Secretary of the Air Force to be President of the University of Texas at El Paso," Wilson, 58, said on Twitter.

"It has been a privilege to serve with our #Airmen -- I am proud of the progress we have made to restore the readiness & lethality of #USAF."

The announcement came after the university published Wilson's name as the sole finalist among candidates for the position.

Wilson will leave on May 31, allowing for a "smooth transition" that would ensure the Air Force's interests are represented before Congress, she said in a letter released by the Pentagon.

She added that the Air Force had cut red tape, got better value for money and had strengthened its ability "to deter and dominate in space."

On Twitter, Trump congratulated Wilson for her university position which, he said, would take effect September 1. "Heather has done an absolutely fantastic job as Secretary of the Air Force," the president said.

Her departure leaves a new high-level Pentagon opening as Trump has not yet nominated a replacement for Mattis. Patrick Shanahan, who served as deputy under Mattis, is the acting defense secretary.

Wilson is a former New Mexico congresswoman who cut short her career as an Air Force pilot when she was named a Rhodes Scholar to study at Oxford University in England.

Descended from a family of fighter pilots, she became the top civilian official in the Air Force two years ago, after previously serving as a university president.

Wilson's announcement came on the same day that White House Communications Director Bill Shine resigned, with plans to advise Trump's 2020 re-election campaign.

He and Wilson are the latest of many administration staffers and cabinet members to leave since Trump's tumultuous term began in January 2017.