Originally trained as an architect, he has worked in architectural practice and as an independent consultant, researcher and writer. He is a member of the Peer Review College of the Engineering and Physical Sciences Research Council, and a regular reviewer for the Technology Strategy Board. He is a regular referee for the journals Building Research & Information, and Design Studies.

Dr Macmillan’s research interests lie in three main areas. First, the tangible and intangible benefits of a well-designed built environment, including its effect on social, economic and environmental outcomes and the different sorts of value that it delivers – whether use value and social value, or cultural value and image value. The second area is concerned with technological innovations particularly to support low energy buildings, such as smart controls, ergonomic interfaces, renewable energy sources, intelligent facades, and combined heat and power systems. The third area is in improvements in the project process, such as interdisciplinary collaboration and effective teamwork, the application of techniques like whole life costing, through to the development and implementation of tools such as Building Information Modelling (BIM)