Theresa Mintle, Mayor Rahm Emanuel's Chief of Staff since the start of his administration, will step down next month.
Mintle will be replaced by Chief Operating Officer Lisa Schrader.
"Theresa has been a trusted advisor and critical member of my administration from the start, serving with integrity and standing at the forefront of every success, including the 2012 NATO Summit, as well as streamlining city departments and services, and implementing key government reforms to eliminate waste and abuse," Emanuel said in a statement. "Theresa has been an invaluable part of my team and the successes we have achieved would not have been possible without her leadership. I wish her the very best."
The Chicago Sun-Times' Fran Spielman reported that Mintle's decision was heavily influenced by the recent death of her father.
Emanuel described Schrader has a "strategic thinker and problem solver."
Before taking the job with a nearly $175,000 annual salary, Mintle served as chief of staff for Chicago Transit Authority Board Chairman Terry Peterson. She's also worked in government relations with the CTA and spent a year as Vice President of Corporate Development for The Aspen Institute, a Colorado think tank.