Jon Sharpe, chief executive of Europe at VMLY&R, has left the company during a disciplinary process.
Sharpe had only taken the job of running the agency, created from the merger of VML and Y&R, 10 weeks ago.
In a statement, VMLY&R said: "Jon Sharpe has resigned from VMLY&R during the course of a disciplinary process and while suspended from the company. Following reports received from employees, a formal investigation was launched using external counsel.
"As a business, we have procedures to ensure people can speak up in confidence and to protect the anonymity of those who raise concerns we will not provide further details."
Sharpe was a former chief executive of Y&R London before being made chief executive of VML Europe when Paul Lawson replaced him in November 2017. Lawson, along with chief creative officer Jonathan Burley and managing director Katie Lee, were later ousted after the merger of the two agencies, leaving Sharpe in charge.
Lucy Taylor, VMLY&R's head of marketing and new business, has also left the business.
Sharpe told Campaign: "I have resigned from VMLY&R to pursue new opportunities. I strenuously deny the reports received and have vigorously defended myself against them. I will be making no further comment at this time."