The partnership behind the Corrib Gas project is to invest another €800m to bring it to completion between now and late 2014.
Shell E&P Ireland claims the investment will create 700 direct jobs and 750 indirect jobs in that period.
It also said when complete the project could supply up to 60% of Ireland's gas needs at times of peak production.
A spokeswoman for Shell to Sea said Shell's claim that it would sustain more than 1,400 jobs did not stack up and was not believable.
Maura Harrington said most of the construction work on the project had now finished and the few jobs that will continue were not long-term, sustainable, or worth the damage done at a local or national level.
She said: "The project should be stopped until there is a proper return for the people of Ireland from Irish natural resources."
The controversial project has been under construction since 2004 and trenchant protests from groups opposed to the project has kept it in the headlines since.
However, seven years on Shell will soon begin the final phase of the project. This will involve the construction of a 4.9km tunnel under Sruwaddacon Bay in Mayo.
The company says this means further investment and "continued high levels of employment" in northwest Mayo.
Managing Director of Shell E&P Ireland Michael Crothers confirmed that it will spend another €800m on completing the project by late 2014.
The sea bed wells and pipeline are complete and the terminal is almost complete.
The final phase of work will focus on connecting the deep sea pipe to the terminal via a second pipeline to be contained in a tunnel under Sruwaddacon Bay.
