The agreement is with lead contractor JKC Australia, a joint venture between Japan-based JGC Corporation and Chiyodoa Corporation along with Kellogg Brown & Root.
The scope of work comprises the erection of piping, mechanical and structural steel for the utility and offsite area.
Work will start immediately and is due to be completed by mid-2016.
Monadelphous had called a trading halt on Friday, pending the announcement.
Managing director Rob Velletri said the company was pleased to be participating in one of Australia's world-class gas projects.
Monadelphous has been one of the most successful resources-focused engineering companies.
It grew rapidly during the past mining boom and is moving that expertise across to the oil and gas sector.
