PAS is part of the Local Government Association and provides advice, support and training on planning and service delivery to councils.
Lester is moving to the London Borough of Brent in mid-October where she will become head of planning, transport and licensing.
"I feel like I’ve done a really good job and moved PAS to a place where it’s earned the trust and respect of the sector and, after almost 12 years, it’s time for me to do something else," she told Planning.
"Local government is my history - my blood. I’ve always felt that it’s the right thing to do to go back to the front line."
Before joining PAS, Lester worked in local government for 20 years. After graduating from London University College’s Bartlett School of Planning, she worked at the London Boroughs of Westminster, Camden and Islington.
She said she is looking forward to "exciting and challenging" times ahead at Brent, where she also lives.
"The job will be to influence improvements, and I will have an interest in making Brent a great place as a resident as well as professionally."