The High Court unanimously ruled that the ACT's laws were inconsistent with the Federal Marriage Act, and were therefore unconstitutional.
The ruling is a victory for the Commonwealth, which had launched the appeal against the laws.
But Craig Berry and his partner Ulises Garcia, who were among 31 couples who tied the knot on Saturday, are saddened by the ruling.
After five days, their marriage will be annulled.
"We're sad, but as far as I'm concerned my love for Uli hasn't changed, we're still married as far as we're concerned," Mr Berry said.