Spie has bought 60% of Matra Nortel and will progressively increase its shareholding until it owns 100%.
Matra Nortel has an annual turnover of about £150m and has 1400 staff, 40,000 customers and 36,000 service contracts.
Amec owns 46% of Spie and has an option to buy the rest of the company in 2002.
Amec already has a global alliance agreement with Nortel Networks to support it and its clients in Europe, North America, Australia, the Middle East and Asia. Amec said Spie's acquisition would complement that agreement.
Nortel Networks and defence supplier EADS each have a 20% stake in Matra Nortel.