Deputy Director Carrie Hessler-Radelet will fill the director's role on an acting basis. She has been deputy director since June 2010.
Williams said in a release posted on the agency's Web site he has informed President Barack Obama of his decision to resign effective Sept. 17. The married father of two sons didn't provide any details about the personal reasons and family considerations that influenced his decision.
"The Peace Corps is a stronger and more vibrant agency because of your global leadership and support of the ideals of service envisioned by our founder, Sargent Shriver," Williams said in his resignation letter to the president. "Serving as the director of the Peace Corps has been the highpoint of my career in public service. Thank you for providing me with the opportunity to lead such an inspiring and significant mission."
Williams was appointed to lead the Peace Corps in July 2009 and was sworn in the following month.
The release touted reforms during Williams' tenure that the organization said provide for "a comprehensive analysis to ensure the agency is maximizing its resources and strategic focus to better serve people around the world." It also noted the volunteer organization has expanded into new countries such as Sierra Leone, Indonesia, Colombia, Tunisia and Nepal with Williams at the helm, and has partnered with the Special Olympics, the U.S. President's Emergency Plan for AIDS Relief, the President's Malaria Initiative and Feed the Future.