The William Penn Foundation's new leader will leave Aug. 31 after six months on the job.

Peter J. Degnan, who came to William Penn as managing director at the beginning of March from his post as vice dean of finance and administration at the Wharton School, has tendered his resignation, foundation leaders said Monday.

There will be no search for a replacement. Laura Sparks, previously chief philanthropy officer, will step into the top job, being retitled executive director, when Degnan leaves.

Sparks said Monday that although Degnan's departure was "unexpected and unfortunate, we have an opportunity to build on the continuity" of her tenure. "From my perspective, I have a really good relationship with the board and the family, and am eager to move forward."

The William Penn Foundation is the city's largest foundation with a local focus since the move of the Pew Charitable Trusts to Washington over the last few years, and its shift away from pure philanthropy into research and advocacy. Degnan had been brought in to establish stability after changes in grant-giving guidelines and the sudden departure of activist Jeremy Nowak, who left William Penn in 2012 after heading the foundation for 2½ years.

David Haas, the foundation's board chairman, declined Monday to say exactly when Degnan shared his intention to resign, saying only that it was "within recent weeks." The board accepted his resignation Monday, he said, and he is not immediately taking another position. Haas also declined to make Degnan available for an interview.

He said Degnan, 55, was leaving for "personal reasons." Asked whether the phrase meant reasons in his personal or in his professional life, Haas declined to say.

Haas said he felt he had a "very good working relationship" with the former Wharton administrator. "He was very focused, very energetic, and very committed and smart, and our institution, as we've grown, we have not attended to the finance and IT systems needs of an institution of our scale, and he brought energy to that."

The change in title of the chief administrator from managing director to executive director signals that Sparks' portfolio will be larger than Degnan's, Haas said. Degnan managed the foundation's investments and finances and operations. Sparks will oversee those areas, while continuing her previous charge of supervising grant-making.

Degnan was not working under a contract of a specific length, according to Haas, nor will Sparks.

Sparks joined the William Penn Foundation in 2012, and as chief philanthropic officer has channeled the philanthropic wishes of the Haas family into the concrete business of awarding $90 million in grant money annually.

Over the last two years, William Penn has awarded 425 grants totaling $204 million, including $45 million at Monday's board meeting. Broadly speaking, the foundation's three main areas of giving are education, watershed protection, and arts and culture. Sparks said she saw no change in direction. "Our strategic areas are set," she said. "Over the last couple of years we've laid some important groundwork, and we are eager to learn from these initial grants."

As an example, she said William Penn had awarded $35 million to 50 groups involved in watershed protection work, and through increased communication and coordination of those efforts, hoped that "as that work evolves, we can figure out how to make it higher-impact."