Inpex said it finished a project started in August 2012 that involved the disposal of more than 560 million cubic feet of rock and sand from Darwin Harbor in the Northern Territory.
The dredging was needed to create a shipping channel and loading area for vessels used to transport liquefied natural gas.
"Without dredging, the project would not have been able to progress marine construction work on the module offloading facility and jetty, which are critical pieces of onshore infrastructure," INPEX Dredging Manager Harutoshi Usui said in a statement.
The company said the dredging campaign had "only a few minor [environmental] impacts" on the Australian harbor.
Inpex is a partner with French energy company Total in the $34 billion Ichthys liquefied natural gas project in Australia.
The offshore central processing facility and the floating, processing, storage and offloading vessel for Ichthys will be among the largest in the world. The installations associated with the LNG project will eventually produce 4.2 million tons of gas each year.
First gas production is expected by 2016.