The 29-year-old's deal will also keep him at Super Rugby club New South Wales Waratahs for four years, Rugby Australia said on Saturday.
"I'm really grateful to Rugby Australia and the Waratahs for all they have done for me," Folau said in a statement issued by the governing body.
"When I made the switch to rugby five years ago, I could never have dreamed that it would have gone this well.
"The World Cup is a big target of mine this year and I believe this Wallabies group can go a long way if we keep on improving.
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"I'm looking forward to working hard and doing whatever I can to help the team achieve what we want to achieve both this year and into the future."
(Reporting by Ian Ransom; Editing by Christian Radnedge)
