The complex is being developed jointly by Saudi Industrial Investment Group and the US' ChevronPhillips Chemical Company.
MMG was awarded the deal by Japan's JGC Corporation, which is the engineering, procurement and construction contractor for the ethylene cracker and downstream units.
South Korea's Daelim Industrial Company is the contractor on the polyolefins package.
The work is expected to be completed by the middle of 2011. It follows the award of a construction sub-contract for offsites and utilities to MMG by Daelim last year.
MMG specialises in oil, gas and petrochemicals projects. It has worked on the Ras Tanura Sea islands and Juaymah platform upgrade and offshore works, and on the Saudi Aramco polypropylene and monoethylene glycol projects at Rabigh.