The Aberdeen-based firm will carry out engineering modifications and upgrades to the Kollsnes facility, west of Bergen.
The contract was awarded by Statoil on behalf of plant operator Gassco.
Wood Group Mustang Norway has already started work on the project, which will last through 2017.
The scope of the contract includes front-end engineering design as well as work on updating electrical, instrumentation and control systems.
The Kollsnes plant processes natural gas from the Troll, Kvitebjorn and Visund fields in the North Sea and provides almost 40% of Norwegian gas deliveries.
The modifications will expand its capacity to accommodate increased production from the Kvitebjorn platform in the North Sea.
When modifications are complete the Kollsnes facility will be one of the largest gas processing plants in the world, with capacity to process 144.5 million cubic metres per day of gas, and will help to ensure the commitments Statoil has for gas deliveries to Europe.
The Kollsnes plant is owned by Gassled. Gassco is the operator and Statoil is the technical service provider.