Mr. Kelly said he will devote more of his time to the New York office, where he once served as president. He will also be tapping Exec VP-Managing Partner Barry Silverstein, who will oversee strategy, Finance Director Nancy Kapplow and Lynn Power, exec VP-group account director, who will oversee new-business efforts. John Staffen, Arnold Worldwide's chief creative officer and managing partner, will lead the office.
Ms. Maroun joined Arnold last May from Y&R North America, where she was a managing partner. Her plans are not known.
"Mary is a true professional, and it's been a pleasure working with her over the past year," Mr. Kelly said. "This is a decision that Mary and I reached mutually, and I wish her only the best going forward."
The New York office serves clients such as Hershey's, Reeses, McDonald's, Lee Jeans and GlaxoSmithKline's over-the-counter diet drug Alli.