Bennett, who will make the switch in January 2007, will help drive what BaxterStorey chief executive Alastair Storey called the group's "steady expansion plan".
He joins existing managing directors Mike Smith and Noel Mahoney in an effort to retain the close link between board members and a growing client list.
"We're delighted to sign him," Storey said. "We needed someone else to ensure we had enough capacity to cope with the growth."
Organic annual turnover growth is about 20% at BaxterStorey but Storey said it was not actively pursuing acquisitions. "Of course we are open to the right deal but an acquisition will not necessarily add much to our business model."
Bennett is one of six top Compass executives due to leave the group in the next few months as part of a major restructure.
By Tom Bill