Stewart has more than 20 years-experience at director level, including roles leading national and regional frameworks.
He joined Tilbury Douglas in 2014, prior to this he was the Northern business development director at ISG.
In addition, he previously held senior roles at Morgan Sindall and Allenbuild.
In his new role, he will focus on supporting national and regional frameworks, key bids, supply chain partnerships and national clients, as well as co-ordinating marketing, events, awards and conferences.
Craig Tatton, Managing Director – UK Building at Tilbury Douglas, said: “Due to his extensive experience, and proven track record within the construction sector, Don is well placed to focus on delivering national initiatives and key objectives, supporting me in the strategic leadership of the UK Building business.”