The move will see around 1,800 Spie employees get new bosses by the end of this year.
Spie UK generated turnover of around £200m last year and its French parent company has been considering a sale since April.
The Imtech deal will see Spie fully exit the UK market.
Gauthier Louette, Spie Chairman & CEO, said: “After a thorough strategic review of our UK operations, we have come to the conclusion that Spie UK would enjoy better perspectives under new shareholding, and we are confident that the ownership of Imtech will bring a robust growth to the combined UK businesses.
“We wish well to our British colleagues, who have always shown dedication and resilience over the years.”
Rob Goodhew, CEO of SpieUK Limited, said: “Spie UK has developed cutting-edge expertise that fully meets the needs of our clients and joining the operations of Imtech is a great opportunity for us to capitalize on our strengths and further develop the business.”
