The acquisition is subject to the approval of Halcrow shareholders and the High Court but is expected to be rubber-stamped by next month.
Halcrow has 6,000 employees and enjoyed a turnover of £465m in 2010.
CH2M Hill is a global engineering firm and came to prominence in the UK market with its role alongside Laing O’Rourke and Mace as Olympic Delivery Partner.
CH2M HILL Chairman and CEO Lee McIntire said: “This acquisition is a game changer for our clients.
“Our global footprint will be deeper and our bench strength will be even more robust. By combining our resources and leveraging our collective technical know-how, we will set a new standard for the marketplace.
“Best of all, our two firms are ideally suited in terms of cultures, markets, geographies, and we have a shared long-term vision for the future.”
Peter Gammie, Halcrow’s chief executive said: “The board’s decision to approach CH2M Hill to discuss the sale of Halcrow is the culmination of a business relationship going back many years.
“We have worked together on many occasions and have become very much aware of each other’s strengths and working practices.
“The consolidation, which reflects an increasing trend in our industry, will create a very significant value proposition for clients.
“We are very complementary in terms of our skills and our markets so, where we share geographies, we are reinforcing one another rather than duplicating.
“CH2M Hill shares the same culture, the same commitment to delivering excellent work, the same dedication to clients; and the same focus on integrity, honesty and respect.
“CH2M Hill is an ambitious and progressive company with strong growth plans, and I see great opportunity for employees and for Halcrow as a business.
“We are currently in the process of sharing this news with our employees and industry partners. We also remain fully focused on our clients and on their day-to-day requirements for the delivery of their projects.”
With the addition of Halcrow’s operations in Europe, the Middle East, Asia Pacific and South America, CH2M HILL will more than double its international presence to almost 30,000 employees globally including over 11,000 outside of the US.
