The Baldwin School, a private girls' school in Bryn Mawr, announced Saturday that a former White House Fellow who is a national security expert will be its next head.

Marisa Porges, 37, will replace Sally M. Powell, who is retiring in June after leading the school for 10 years.

A 1996 Baldwin graduate, a Penn Valley native, and a former naval flight officer, Porges was recently a White House Fellow to the National Economic Council.

She holds a bachelor's degree from Harvard, a master's from the London School of Economics, and a doctorate from Kings College London. Porges writes and speaks frequently on topics such as the Middle East, policy and politics, and terrorism and counterterrorism.

Terry Steelman, chair of the Baldwin's board of trustees, said in a statement that Porges "personifies the visionary women that Baldwin graduates - women capable of leading on the global stage and making a lasting impact on the world. She will bring to the Baldwin School proven leadership abilities, a strategic vision for Baldwin's future, a clear commitment to the vital and transformative nature of a Baldwin education, and great personal warmth."

Before being named a White House Fellow, Porges was an International Security Program Fellow at the Harvard Kennedy School's Belfer Center for Science and International Affairs and an International Affairs Fellow at the Council on Foreign Relations.

For those positions, she traveled throughout the Middle East and Afghanistan. As part of her research on counterterrorism, she interviewed former members of al-Qaeda, the Taliban, and Syrian rebels to understand their perspectives.

In a statement announcing her selection as Baldwin's eighth head, Porges said: "I've always believed Baldwin's approach to education is so effective at shaping young women as future leaders because it instills in its students the confidence, tenacity, and independent thinking that bring lasting personal and professional fulfillment."

She said she was looking forward to working with Baldwin's teachers and staff to provide students with "the same kind of transformative Baldwin experience that served me so well."

Porges and her fiance, Scott Moore, plan to move to Bryn Mawr from Washington this summer.

Baldwin has 572 students. Tuition ranges from $15,000 for half-day prekindergarten to $35,335 for 12th grade. 215-854-2789