Arnold Worldwide said Robert LePlae will join the Boston ad agency as global president, starting Sept. 15.

Arnold said it has grown by 70 percent in recent years, due partly to steady growth by such clients as Dell, Hershey Co., Jack Daniel’s, Unilever, and Volvo.

The agency said LePlae’s appointment is part of an effort to advance Arnold’s international expansion.

LePlae most recently served as North American president at McCann Erickson. Previously, he spent 11 years at TBWA/Chiat Day. Reporting to Arnold’s chief executive, Andrew Benett, LePlae will divide his time between the Boston and New York offices.