Matt Vickers attended the Voluntary Euthanasia Society's presentation of the petition today, which had some 9000 signatures and called on lawmakers to renew discussion about the right to die.
"Obviously when we got the ruling from the judge ... he was quite clear that it was for Parliament to change and that there was good reason for them to do so," Mr Vickers said.
"My wife showed a lot of courage taking this to the courts. As a result of that we built up a huge groundswell of support across New Zealand."
Individual MPs from the Green, Labour, National and Act parties attended to show their support.
"In some ways it should be beyond party politics," National MP Chris Bishop said.
A counter-demonstration of people opposed to euthanasia also gathered at Parliament.
Family First New Zealand director Bob McCoskrie said he was concerned the "right to die" would become a "duty to die" for vulnerable people including the elderly and disabled.
Ms Seales, who had a brain tumor, was unsuccessful in seeking a High Court ruling that would let her doctor help her die without criminal prosecution.
The Wellington lawyer died of natural causes on June 5, shortly after her family and lawyers received the ruling.
