One of the lead campaigners behind Ireland's historic same-sex marriage referendum has urged Prime Minister Malcolm Turnbull and parliamentarians not to go ahead with a plebiscite, warning the experience was "brutal" for gay and lesbian people and their families.

Grainne Healy, co-director of the Yes Equality campaign, said Irish volunteers needed counselling after abuse and hate speech from reform opponents, calling for MPs to stop Australia from seeing an unnecessary plebiscite campaign.

In a letter to all MPs, Dr Healy said a plebiscite on same-sex marriage would bring about hurtful and divisive commentary under the guise of fair debate.

"The 'no' side posters which declared that 'every child deserves a mother and a father' were deeply hurtful and upsetting for LGBT-headed families as they passed the posters on lamp posts and billboards across the country - explaining to our children that they were OK and trying to hide the posters from them was awful for LGBT parenting families.