The Australian Capital Territory Supreme Court approved solicitor Mark McCormack's application to use the social networking site to serve a foreclosure notice on the couple following several failed attempts to contact them at home and by email.
McCormack, who was representing the lender MKM Capital, said that the defaulters' Facebook accounts included their names, dates of birth and listed each other as "friends", which was enough to convince the court that they were the right people.
Neither defendant had engaged the privacy settings on their Facebook profiles, which allowed strangers to view their pages.
The judge ruled that the documents must be attached to a private email sent via Facebook that could not be seen by others visiting the defendants' profiles.
McCormack, who is a keen Facebook user, said using the social networking site to contact people was the logical "next step".
He said: "I think the courts will continue to adopt it on a case-by-case basis. They will [just] need to assure themselves that it is reasonably likely to bring [the court's decision] to the attention of the parties concerned."
Australian courts have given permission in the past for people to be served via email and text messages when it was not possible to serve them in person.
McCormack claims this new ruling is a world first.
Facebook said in a statement: "We're pleased to see the Australian court validate Facebook as a reliable, secure and private medium for communication.
"The ruling is also an interesting indication of the increasing role that Facebook is playing in people's lives."