Stewart joins after a brief spell as a director at Lumsden & Carroll and he was at Allenbuild for nearly ten years before that.
ISG has created the new role for Stewart in a bid to take a greater share of work in the region.
He will lead a team covering an area stretching from North Nottinghamshire to the Scottish borders and encompassing Yorkshire, North Lincolnshire, Humberside and the North East.
Sectors being targeted include education, leisure, commercial and retail and Teesside and Tyneside have been highlighted as potential growth areas.
Stewart said: “The range and depth of ISG’s experience makes this a dream business development role because we have the expertise in-house to respond to almost any brief and develop cost-effective, workable solutions to address any construction challenge.
“I’m joining an ambitious and dynamic team and am looking forward to becoming part of the ISG success story as the company continues to grow.”
Joe Webb, ISG director, added: “There is a real opportunity to enhance the visibility of the ISG brand outside of its core regional markets and Don will spearhead our approach to major private and public sector clients within these areas.
“Despite the economic backdrop, there remains strong demand for those contractors able to demonstrate a consistent and high quality service offering, regardless of geography, and Don’s team will play a critical role in assisting the business in converting these opportunities.”