The three-year contract, agreed to in June 2013, will be extended until December 31, 2017 with two further 12-month extension options.
The scope of the contract variation is for the ongoing supply, maintenance, storage, transport and handling of all scaffolding equipment on the North West Shelf's onshore and offshore locations.
GCS also supplies specialist management and labour resources to Woodside under its Karratha-based subsidiary, GCS Integrated Services.
"We are pleased this contact has been extended to December 31, 2017, as it is testament to the quality of the products and services GCS has been providing Woodside over the past two years, managing director Enzo Gullotti said.
GCS is also supplying scaffold equipment to Kaefer for the Ichthys LNG project in Darwin, and last month secured a new two-year contract with CITIC Pacific Mining's Sino Iron Project in northern WA.
Revenue streams in residential and resources sector make up about one-third of GCS' income.