Costain and May Gurney have announced merger plans.
The companies will have combined revenues of £1.6 billion and challenge rivals including Balfour Beatty and Carillion.
Major infrastructure contractor Costain, which is working on London's Crossrail underground rail tunnel, is based in Maidenhead, which will be the group's headquarters.
The group plans to retain May Gurney's headquarters in Trowse, Norwich, as a shared services base.
May Gurney has around 800 of its workforce in Norfolk.
More top news
The Suffolk PCC has called for tighter EU border controls after a convicted paedophile banned from the UK was jailed for the second time
Pupils at a school in Norwich have been cooking their own home grown produce after turning parts of the playground into a garden
Exhibition tells the story of Sir Ernest Shackleton's mission to "bring every man home"