The judges found the ACT laws could not operate alongside federal laws as only the federal parliament had the power under the constitution to legislate on same sex marriage.
They said the Marriage Act does not allow or recognise marriages between same sex couples.
The court held the ACT Act provided for marriage equality for same sex couples.
Not, as the territory argued, for a form of legally recognised relationship which was different from marriage.
The finding means ACT Act cannot operate concurrently with the federal Act.
"Because the ACT Act does not validly provide for the formation of same sex marriages, its provisions about the rights of parties to such marriages and the dissolution of such marriages cannot have separate operation and are also of no effect," the statement said.
"The Court held that the whole of the ACT Act is of no effect."
So, all those happy couples who got married yesterday have just had their marriages declared invalid.
But while bigotry and hate have won today, this isn't over. The majority of Australians support marriage equality. And they're going to keep pushing for it until their bigoted federal politicians catch up with the modern world.