The new division will combine the existing Energy & Process and Environment operations and be run by managing director Mark Rogerson who joined Costain from Serco earlier this year.
The Natural Resources division will operate alongside the Infrastructure division, which will now also include all power sector activities.
The Infrastructure division will continue to be led by Managing Director Darren James.
Alan Kay, previously managing director of the Environment Division, will take on the new role role of Group Technical & Operations Director on the Executive Board.
Charles Sweeney – previously Managing Director of Energy & Process – has left the company after nine years to “pursue opportunities elsewhere”.
Andrew Wyllie,Costain Group Chief Executive, said: “As part of the planned transformation of Costain we have formed this new Natural Resources Division committed to delivering an innovative and integrated service across engineering consultancy, construction and operations and maintenance.”