The development is estimated to be worth £200m to the Shetland economy
The first commercial gas from the west of Shetland is to be piped ashore to the Scottish mainland, after a deal was reached between Total and the council.
The development by the French oil company is estimated to be worth £200m to the Shetland economy.
The council secured a deal to lease land to the firm and a small royalty on the gas going through the new plant.
Work is to start next month on building a new gas processing plant next to the Sullom Voe terminal, creating 700 jobs.
The 700 construction posts will be short-term, but when the plant is up and running in 2014 it will employ about 70 permanent staff.
Total said the investment would help open up the Atlantic frontier for future gas development.
The project is part of a £2.5bn investment by the firm to pump gas ashore to help heat homes across the UK.