Aren Platt, a top aide to Mayor Cherelle Parker, is resigning less than one year into her administration

Chief Deputy Mayor Aren Platt, a close confidante of Mayor Cherelle L. Parker and an architect of her historic campaign, is resigning from the administration, Parker’s office announced Thursday.

Platt’s departure less than one year into the new administration is a shocking development that is being received by many in City Hall as a sign of significant discord within the mayor’s office.

Parker said in a statement she was “accepting the departure … with deep gratitude and understanding.”

“I wouldn’t be here but for [Platt’s] work — as senior campaign adviser and now as one of my two chief deputy mayors in my administration,” Parker said. “I’ll be forever grateful to him. But now it is time for Aren to pursue his career opportunities outside city government, and I am fully supportive of this decision.”

The mayor’s announcement did not specify what Platt will be doing next.

“I will be leaving a job that I love that may be the best job that I’ve ever had, working for the most visionary and dynamic Mayor of my lifetime,” Platt said in a statement. “Mayor Cherelle Parker has shown that the work will guide us and the results will be what transforms the City. And while I will no longer be in City government, I will always be the biggest cheerleader for this Mayor, for the administration, and for the City.”

Platt will leave city government Oct. 25. Upon his departure, Vanessa Garrett-Harley, the city’s chief deputy managing director for children and families, will become chief deputy mayor for social impact and strategic initiatives.

» READ MORE: Meet the staffers who ran Cherelle Parker’s historic campaign and will lead her mayoral administration

Parker came into office with an unusual structure for the top rung of her administration by naming a trio of top aides she referred to as her “big three”: Platt, Chief Deputy Mayor Sinceré Harris, and Chief of Staff Tiffany Thurman. Parker deliberates with all three when making major decisions, but the aides each have their own portfolio.

Platt led “planning and strategic initiatives,” and his areas of focus included communications and planning and development. Several initiatives under those areas have had rocky rollouts.

Platt at one point played a central role in the administration’s handling of the 76ers’ controversial proposal to build a new arena in Center City. But recently, Thurman has emerged as Parker’s point person on the issue.

Parker has promised to unveil a major policy proposal this fall to accomplish her goal of building or preserving 30,000 units of housing during her first term, an endeavor that falls under Platt’s portfolio. But the plan has not been announced, and the city’s director of planning and development, John Mondlak, is still serving on an interim basis nine months after Parker took office.

And in the early days of the administration, a new communications policy that required all public statements from city agencies to be approved by the mayor’s office was widely criticized.

» READ MORE: Inside Cherelle Parker’s winning campaign for Philly’s Democratic mayoral primary

A political operative and fundraiser with years of experience in state politics, Platt first entered Parker’s inner circle around 2015 when he helped her navigate the ongoing fallout from her 2011 arrest for driving under the influence when she was a state representative. The Mount Airy native briefly left politics to work as a top aide to the CEO of La Colombe. But he remained close with Parker, and in 2020 he was among the small group of confidantes with whom Parker first discussed running in the 2023 mayoral election.

Platt and Parker were seen as fiercely loyal to each other. She gave him a special acknowledgment during her victory speech on the night of the May 2023 Democratic primary, a win that ensured she would become the first female mayor in Philadelphia’s then-341-year history.

“The toughest time that I have ever had in my professional and personal life — and I had to deal with it publicly back in 2011 — and that was the DUI,” Parker said during her victory speech. “It was Aren Platt who was the adviser who helped me through those difficult times.”

Staff writer Anna Orso contributed to this article.