The engineering group WS Atkins is buying the US design firm PBSJ for $280m (£176m) in a deal which "balances the company's geographic presence" and "deepens technical skills in established sectors".
Atkins, which has 200 engineers working on the 2012 Olympics development in east London, will finance the acquisition from cash reserves and a new four-year £150m facility.
The deal will help the group to manage looming public spending cuts in the UK by reducing the proportion of work in Britain from 70 per cent to 50 per cent.
Keith Clarke, the Atkins chief executive, said: "This is an important acquisition and forms part of our plan to grow our business through a multi-skill, multi-local strategy."
The share price closed up 4.4 per cent at 31.5p.
PBSJ saw underlying earnings of $47m last year and employs around 3,500 people in the US.