Prior to the negotiations, 100% of Monadelphous' workforce at project were casual.
It took months for a coalition between the Australian Workers Union and the Maritime Union of Australia, known as the Offshore Alliance, to come to an agreement with Monadelphous.
Last September the contractor faced multiple ‘protected action' strikes from union members who protested pay and working conditions.
One of the key concerns from unions was that workers could be stood down without pay when operations were disrupted by weather events, for example cyclones.
Finally, in November Monadelphous came around to union demands for higher wages, more secure jobs and better working conditions.
Union members voted in favor of the new EBA last month. The agreement was then ratified by the Fair Work Commission this month.
"Our members' families will reap the benefits of knowing that they can secure a bank-loan, plan a holiday and be confident of paying the bills," the unions said in a joint Facebook statement.
"The Offshore Alliance want as many of our members as possible to have the opportunity of having secure jobs. This means permanency without pay-cuts."
The unions flagged they would push for similar changes at Woodside Petroleum and Chevron Corporation operations.
Monadelphous was contacted for comment.