Costain has acquired Rhead Group, a professional services consultancy, for a total of £36m.
Rhead Group’s 550 staff will join Costain’s power sector by the end of the year, reporting into the natural resources division.
The company’s senior management team, including Rhead Group’s chief executive Nigel Curry, will remain with the business.
Rhead Group was set up in 1985 to provide a range of solutions for infrastructure, construction and asset management programmes, mainly across the UK.
It also has offices in the Middle East and Asia Pacific.
The consultancy works with a number of blue chip companies including National Grid, Wales & West Utilities and BAE Systems.
For the year ended 31 July 2014, Rhead Group posted revenues of £63.5m and an EBITDA of £5.2m.
Costain chief executive Andrew Wyllie said: “This transaction accelerates the development of Costain and further broadens our range of capabilities to meet the requirements of major blue chip customers, providing greater ability to deliver integrated solutions across the full lifecycle of a project.”