Peter Long takes up the post on 1 April, but became chief executive-designate on 7 February. Sixty-year-old MacKenzie will retire in November.
Long, 53, was a non-executive director of Bryant Group for two years. Between 1995 and 1999, he was a director of Rugby Group with responsibility for the firm's worldwide joinery and US building products businesses.
He was previously chief executive of Bowater Packaging's industrial division.
Bryant is also looking for a finance director to replace Michael Chapman, who resigned yesterday after the company's interim results. John Dennison, finance director for Bryant Homes, will stand in until a replacement is found.