Richards has led the sixth-largest public transportation agency in the U.S. since January 2020.
"It has been an honor to lead SEPTA, and especially to lead our 9,500 employees, each of whom brings incredible expertise, dedication and heart to serving our community," she said in a statement.
SEPTA Board Chair Kenneth Lawrence says the transit agency will conduct a nationwide search for Richards' successor. This process is expected to begin in the coming weeks.
Richards' last day is November 29.
"Leslie has been a dedicated public servant for nearly 20 years, and at SEPTA she has been a true champion for public transit and for our region as a whole," said SEPTA Board Chair Kenneth Lawrence," said Lawrence.
Chief Operating Officer Scott Sauer will serve as interim general manager until a permanent successor is chosen.