It follows the company being awarded preferred contractor status in October.
The five-year contract comprises all aspects of mine operations including drill and blast, the removal of around 300 million bank cubic metres of overburden, ore harvesting and equipment maintenance.
Macmahon will operate the fleet, most of it provided by FMG.
The contract takes Macmahon’s order book to a record $3.6 billion.
Chief executive Ross Carroll said the contract was particularly important, given the company’s recent decision to steer away from construction and focus on the more profitable mining side of the business.
“This is an exciting project that builds on the existing success of our surface mining operations, securing a stronger foundation for the company’s mining-focused business over the next five years,” he said.
“Macmahon has a long history of successfully delivering mining projects in the Pilbara and this project further expands the company’s presence in the region.”
The $US1 billion ($A951 million) Christmas Creek expansion will take production at the Chichester operations to 95 million tonnes per annum.
The project is part of FMG’s broader Pilbara expansion to 115Mtpa by the end of the current quarter, and 155Mtpa by the end of the year.
Macmahon has recruited about 600 people for the project, with more than 500 already onsite.
The company said capital requirements were likely to be about $A30 million.
Macmahon recently completed a capital raising of about $80 million.