The move is designed to allow joint chief executive Simon Ward more time for running SP's parent, St Ives Group, in his other role as group sales director.
Ward will retain his position as joint chief executive while Clews will take over much of his customer-facing and operational responsibilities.
"Mark has been with the company for over 15 years," Ward said.
He has risen through the ranks and he understands SP completely. This is great news for us," he added.
The handover will be phased over the next 18 months while Ward takes on more responsibility for the sales and customer-service sides of St Ives Group.
"The bigger we have got, the more demand there has been for this new role," Ward said. "SP is growing at 10m a year and we are aiming for a 100m turnover in three years' time," he said.
SPs general manager promoted to director
SP Group has announced that general manager Mark Clews (pictured) has been promoted to the new position of managing director at the firm.
