Imtech, jointly owned by Dalkia and EDF, agreed a deal with Spie SA in October to acquire its British subsidiary for €50m (£43m).
Dalkia, EDF and Spie SA are all French companies.
Spie SA put its UK operations under strategic review in April this year.
Following fulfilment of customary conditions and regulatory approvals the transaction has now completed and Spie UK is now wholly owned by Imtech.
Gautier Jacob, chief executive of Imtech Group, said: "I am pleased this strategic acquisition has now completed and the reaction from the marketplace, as well as Imtech and Spie UK employees, has been positive. This very much strengthens and accelerates our capabilities to deliver decarbonisation solutions for our clients and we look forward to further developing our business together in the future."
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