Thousands of people have flooded the streets of Dublin for what organisers are hoping may be the last annual summer March for Marriage.
The Government is due to hold a referendum on marriage equality in the first half of 2015.
March organiser Max Krzyzanowski said he is very encouraged by what the polls are showing on the issue and called on the public to turn up and vote on referendum day.
"The only way that this referendum will be lost by the equality side is if people are complacent and they stay home," he said.
He rejected the IONA Institute's argument that it is not discriminatory to give marriage "unique treatment" because marriage between a man and a woman is a "uniquely pro-child" institution.
"Children raised by couples in same sex households do equally as well as children raised in heterosexual households and that argument is a form of scaremongering," he said.
He said allowing same sex couples to marry will have no effect on the sanctity of the institution.
"They can maintain the sanctity of marriage within their religion. That has nothing to do with what we are arguing for here," he said
Mr Krzyzanowski said it is "wonderful" to see the Irish population as a whole come out in support of equal marriage rights.
Rachel Mathews Mackay of SIPTU LGBTQ said there is a huge swell of support for marriage equality all around the country.
"There is nothing for anyone to be afraid of. We are not here to destroy anything, we are just here to be accepted like everybody else," she said.