The project marks emergence of PNG as a gas supplier to Asia and is expected to push economic growth next year to 20 per cent.
Managing Director of Esso Highlands, which manages the project, Peter Graham said coming in ahead of time is 'an exceptional achievement' that 'bodes well for future investment' in the country.
The PNG LNG project has had to contend with some of the toughest terrain in the world to build a pipeline more than 700 kilometres from the PNG highlands, across the Gulf of Papua to Port Moresby.
Mr Graham said the project faced seismic activity, floods, landslides and a complex social environment as well as the usual logistical challenges of building a big project.
"This is a great milestone to have the first cargo in mid-2014," he told Radio Australia.
"I think it will be a hugely exciting day for everyone in Papua New Guinea to see those huge ships sailing in and load up and sail away to the customers.
"It is just a great demonstration of what can be achieved in Papua New Guinea and that is just so important for future investment in PNG as well."
Esso Highlands, a subsidiary of ExxonMobil, said the $US19 billion plant in PNG will supply 6.9 million tonnes of liquefied natural gas a year to customers in Japan, China and Taiwan.
In the past 12 months, some of PNG's other crucial resource projects such as the Ok Tedi copper mine and Newcrest's Lihir and Hidden Valley mines have struggled leaving the government with a revenue shortfall.
The LNG project is the first of a number of gas projects under development in Papua New Guinea.
It will begin operations with 2 processing trains but has talked about building up to 5 - a move that would put it among the largest projects in the world.
But that depends on having the gas.
In the past, Esso Highland's Managing Director, Peter Graham, said he has seen potential for some of that to come from the big Elk-Antelope field in which Total of France and Canada's Inter-Oil have a major stake.
After recent changes in ownership of Elk- Antelope, Mr Graham is coy about whether ExxonMobil will be able to access that gas.
- By Jemima Garrett