Irons said he doesn't "have a strong feeling" about the issue, he "worried" that gay marriage would "debase" the institution.
"I worry that it means somehow we debase or we change what marriage is," Irons said. "I just worry about that."
The 64-year-old actor pondered what same-sex marriage would mean for inheritance taxes. "Could a father not marry his son?" he asked, to pass down his estate without paying a tax.
"Few people will agree with Jeremy Irons’ bizarre 'concerns' about equal marriage," a Stonewall representative told The Independent.
“Sadly his comments do seem to indicate he's taken his role as a Pope in "The Borgias" a little too seriously."
But Irons stepped back from his remarks a bit, saying that he wished "everybody who's living with one other person the best of luck in the world because it's fantastic”.
"Living with another animal, whether it be a husband or a dog, is great. It's lovely to have someone to love. I don't think sex matters at all. What it's called I don't think matter at all."
Stephen Colbert later mocked Irons' in a segment on "The Colbert Report."
"See? He's cool with whatever," Colbert said. "A sexless marriage to a wife, a sex-filled marriage to a dog."