Maurice Williamson, a minister in the conservative National Party government, joked ahead of Wednesday's vote that he had seen "the most enormous big gay rainbow" over his electorate and taken it as a sign to back the change.
He also mocked fears about the impact of the reform, which passed by 77 votes to 44, and revealed critics had written him letters warning he would burn in hell if he did not change his mind.
"The sun will still rise tomorrow... you will not have skin diseases, or rashes, or toads in your bed," he told parliament just before New Zealand became the 13th nation globally to allow same-sex marriage.
"The world will just carry on. So don't make this into a big deal."
The speech has been viewed almost 400,000 times on YouTube -- http://youtu.be/XCA8CA2hUoQ -- and was described as "epic" by the Huffington Post, with Irish pop star Ronan Keating tweeting "everyone should take a listen... simply brilliant".
Another video featuring the public gallery erupting into a Maori love song after the vote was declared has attracted almost 650,000 hits -- http://youtu.be/DW4DXOAXF8U.
The portly, grey-haired Williamson, who is married with three children and describes himself as a "strong right winger" on economic issues, was labelled an unlikely gay icon by 3News.
He told the broadcaster that US chat shows were trying to line him up and he had received messages of thanks and support from all over the world, comparing himself to a kiwi version of Korean pop sensation Psy.
"It's just bizarre," he said. "This is just a speech I went down to the house to deliver. I feel like Gangham Style now, what am I going to do for an encore?"