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 Health Secretary Jeremy Hunt has been visiting one of the region's struggling hospitals the Queen Elizabeth in King's Lynn
There are calls for a fresh inquiry into how thousands of NHS patients were given contaminated blood in the 1970s & 80s.
Video of a bus that got stuck after taking a wrong turn into roadworks in Norwich has gone viral on the internet.