Mr Knight said it also effectively continued a discrimination against a gay or lesbian monarch because any marriage (of the next six in line to the throne) required the consent of the reigning monarch.
"There is an effective continuation of discrimination against them. The consent provisions around marriage are likely to present an impediment to gay and lesbian couples if they are in the line of succession becoming monarchs."
But the biggest discrimination was against New Zealanders, he said.
"Most fundamentally, the great discrimination that lies in this is that it effectively discriminates against Kiwis, against New Zealand because practically there is no prospect of a Kiwi being a head of state of New Zealand under the line of succession."
National Party member and blogger David Farrar also appeared for the Republican Movement and asked the committee to consider amending the bill allowing the monarch to be a member of any religion.
He said there was limited ability for the New Zealand monarchy, which is what the bill was about, to actually reflect what Kiwis wanted.
"If we were designing a New Zealand monarchy based on the heirs of Colin Meads, for example, we would not have a religious prohibition."
It would fit much better the values that New Zealand had. Sean Palmer, the chairman of Monarchy New Zealand, supported the bill. He said the constitutional monarchies had an ability to evolve over time to adapt to circumstances.
"This legislation is a fantastic illustration of that evolution in action."
He said there was no legal or constitutional impediment to an heir to the throne entering into any form of legal marriage in Britain, where gay marriage was legalised this year.
"They certainly do require the permission of the monarch but that permission is granted or withheld on the advice of the Government. ...
"A monarch is not going to simply say 'I don't like the idea of you marrying a blonde woman' ... the monarch is going to look for advice."
What they said
"If we were designing a New Zealand monarchy based on the heirs of Colin Meads, for example, we would not have a religious prohibition."
David Farrar, Republican Movement
"A monarch is not going to simply say 'I don't like the idea of you marrying a blonde woman' ... the monarch is going to look for advice."
Sean Palmer, Monarchy New Zealand