The contract is set to be worth up to £32m to WSP over the next nine years.
WSP has been working with the Bournemouth and Poole borough councils for the past 11 years in a tripartite partnership. It has 30 staff embedded with the councils.
Larry Austin, service director for environment at Bournemouth Council, said: “The appointment of WSP as a strategic partner to deliver engineering professional services for both Bournemouth Council and Borough of Poole comes at a critical time for both authorities in light of ongoing organisational changes. Delivery of our various engineering led services and functions, together with the key projects within the Bournemouth and Poole conurbation, can now be approached with the continued high level of certainty and quality that the elected members, businesses and residents expect.”