"She has no particular great insights into politics, she is a fictional writer. I have great respect for her as a fictional writer [sic]."
Mr Key conceded he had read some, but not all of the Luminaries.
"Obviously it's done phenomenally well and I'm really proud of her, but it would be no different from Richie McCaw or the Mad Butcher or anybody else having a view on politics.
"They're absolutely entitled to do that, but her views on politics are no more authoritative than anybody else's.
"I mean, if it's Corin Dann, and he's the chief political reporter, then his comments carry more weight because that's what he does for a job."
Mr Key previously dismissed Catton's views on the Government as being those of the Greens.
Her comments have attracted the ire of the right, with Radio Live presenter Sean Plunket calling a "traitor" and an "ungrateful hua", a Maori slang word that was widely mistaken for "whore" by listeners.
The Taxpayers' Union meanwhile revealed she had received upwards of $50,000 of public funding in the past few years.
Catton responded to the accusations with a statement on her blog. In it she accused New Zealand's mainstream media of publishing "inflammatory, vicious and patronising" things about her.
In an interview with the Guardian at the weekend, she criticised "the scale and shabbiness of this jingoistic national tantrum", which she said "shames me deeply as a New Zealander".
"I believe it can be countered only with eloquence, imagination, and reasoned debate - qualities that might seem to have disappeared from our national conversation, but that persist, and will continue to persist, despite efforts to humiliate and silence those who speak out."