Under the terms of the deal, Arcadis will hand EC Harris shareholders 3m shares and an undisclosed cash sum.

The deal needs EC Harris partner approval and is expected to be formally signed next month.

EC Harris is now the fourth major UK consultancy to fall into the hands of a foreign firm after Davis Langdon, Halcrow and Scott Wilson all succumbed to offers in the last 18 months.

The merged company will boast almost 19,000 professionals and a €2.3bn turnover.

Arcadis will leapfrog its way through the ranking to become a top five global leader in building consultancy and project delivery services, with close to 6,000 staff in Europe, the US and Brazil.

Philip Youell will continue as chief executive of E C Harris and joins the Arcadis senior management committee.

EC Harris’s current chairman, Richard Clare, will step into a wider strategic client development role in Arcadis while remaining on the EC Harris Board in an advisory capacity.

In a statement both firms said there were no plans for any redundancies as a result of the deal.

Youell said: “This is a unique deal that will accelerate our vision and plans for growth and will enable us to deliver our clients’ goals as well as our own.

“While we have been successful in winning some very large programmes of work and have many more in the pipeline, the demand from our clients is such that we recognised that we needed to grow and develop internationally, at a much faster rate than we are currently doing.”

He added: “We have received a number of approaches from large international companies in the past, but Arcadis is the only one that has been right culturally and strategically for EC Harris, it is an exceptional fit.

“Arcadis genuinely shares a client-first philosophy and a clear vision of the style of business we need to be in order to meet changing client needs. We now have the strength and intention to invest and further develop a leading global built asset consultancy position.”

EC Harris’s well established and rapidly expanding operations in Asia and the Middle East will also provide Arcadis with strong footholds in these markets.

Furthermore, the deal brings Arcadis into the top five consultants in the UK, allowing it to expand its relationships with multinational clients both inside and outside the country.

EC Harris will continue to operate as a partnership, with a company-wide remit within Arcadis, taking up a leadership role in driving the development of programme and project management services.

EC Harris will bring their built asset consultancy approach to the wider Arcadis business, taking a leading role in the UK, Middle East and Asia.

Arcadis CEO Harrie Noy said: “This merger is a major step forward in realizing our strategic ambitions. With EC Harris we get a leading position in project management and related services while their built asset consultancy approach perfectly fits our goal of expanding our services at the high end of the value chain.

“With the expansion of our footprint in the Middle East and Asia we can capitalize on the growth opportunities in these markets. Our strengthened position in the UK market will allow us to provide a wider portfolio of services to the clients of our combined firms. We welcome the strength of the EC Harris brand and the leadership they bring to Arcadis and are excited about the synergy opportunities.”