Groundworks contractor Blanchard Wells and concrete specialist Southern Concrete have merged to create the new business.
The groundworks firm was set up 20 years ago by Mark Wells who seven years later also formed the structures business.
Now joint chairman Wells has decided to combine the companies as jobs become more complex to improve efficiency.
Newly-formed Blanchard Wells Structures and Civils will employ more than 400 workers and has its headquarters in Soberton, Hampshire.
Its order book stands at £25m and its turnover in 2017/18 was £34m.
The original company, Blanchard Wells, was founded in 2000 by Mark Wells and Mark Blanchard. Mark Blanchard’s son Luke is Managing Director of the new company.
Wells said: “We are ambitious and aim to grow. This is a logical step to combine our groundworks expertise with our skills in concrete frames and civil engineering and will make it easier for our customers to do business with us.”