Marriage equality advocates and independent MP Andrew Wilkie brought the case against the move.
They argued the government did not have the right to spend more than $120 million of Treasury funds on the ballot without passing an act through parliament.
The government will draw the money from a fund for “urgent and unforeseen” spending, but critics say the government itself created the urgency with its own deadline for the vote.
The Australian Bureau of Statistics is preparing to mail out the first ballot papers from Tuesday next week.
