English, a committed Catholic, also voted against the earlier Civil Unions Bill which allowed for same-sex relationships to be legally recognised.
"I'd probably vote differently now on the gay marriage issue, I don't think that gay marriage is a threat to anyone else's marriage," he said, according to Newshub.
"Just seeing the impact it's had for couples and the fact that it doesn't actually erode marriage. In some ways it's an affirmation of the concept."
The NZ AIDS Foundation has confirmed that English will be formally invited to attend the Big Gay Out in February, as his predecessors as Prime Minister have been. The Foundation says it extends invitations to all the leaders. The Foundation says it extends invitations to all the leaders of the main political parties and included in that invitation is the opportunity to speak to the crowd from the main stage.