The £470m-turnover firm confirmed it had bought the civil, structural and transport engineering consultant for an undisclosed sum.
Thorburn Colquhoun has 450 staff and earned an estimated £25m in fees last year.
Thorburn Colquhoun chief executive Ian Wotherspoon said the tie-up with California-based URS would give Thorburn Colquhoun the muscle it needed to expand, with the company set to double in size within three years. He said: "The aim is to build a 800 to 1000-strong business either through acquisition or organic growth." He said the company would continue to trade under the same name and no redundancies were planned.
URS has made good on its plan to use a major UK acquisition as a springboard into the single European market.
Last October, URS chairman and chief executive Martin Koffel told City fund managers and brokers that his firm was on the hunt for its first major acquisition as a way of breaking into Europe (9 October 1998). URS is keen to pick up work on major private finance initiative schemes in the UK.
Wotherspoon said the buy-out allowed Thorburn Colquhoun to make a strategic move out of the middle ground. He said: "The deal means that we have the financial backing we need to take on larger contracts, including PFI deals, but also gives us access to the technical skills of 7000 staff worldwide." He said the deal followed a large amount of consolidation in the sector. "The industry is being divided between major players and niche consultants."
- WS Atkins, the UK's largest engineer, has doubled its presence in Ireland with the purchase of Dublin-based McCarthy & Partners. Atkins would not reveal what it paid for the 50-strong firm, which is ranked among Ireland's top six engineers. Atkins has worked with McCarthy & Partners over the past two years, winning work on three public sector infrastructure contracts.
Atkins finance director Ric Piper said: "We've been looking for a possible acquisition in Ireland for some time. We got to know McCarthy & Partners through working with them, and we formed a bond with them. The deal grew from there." Piper said McCarthy & Partners would continue to trade under its existing name. No redundancies are planned.
He said: "We're reasonably optimistic about the future of the Irish market, although it forms quite a small part of the total operations."