Former President Mary McAleese will today call on families to support a 'Yes' vote in the same-sex marriage referendum, aruging that it poses no threat to couples in a heterosexual marriage.
Mrs McAleese, who is a constitutional and canon lawyer and a practising Catholic, is due to make her comments as she addresses an event hosted by the Lesbian, Gay, Bisexual and Transgender organisation BeLonG To in Dublin this morning.
She is expected to talk about her belief that allowing for gay marriage will be good for all society, and will underline the country's commitment to equality.
Last month Mrs McAleese's son Justin publicly came out as a gay man and called for people to vote yes in Friday's vote.
Writing in the Irish Independent, he outlined the difficulties he faced in coming out and said allowing for gay marriage would protect gay children's rights.
"It is about creating an environment where they can discover and come to terms with who they are with the important guidance of their mothers, fathers and family," he wrote.
Mary McAleese is a hugely significant figure within the Irish Catholic community and has described her and her husband, former Senator Martin McAleese, as devout Catholics.
However, she has been an outspoken critic in a number of areas of church teaching and policy.
Last year she was praised by the Irish Association of Catholic Priests when she said she didn't like the church's attitude towards gay people and said the church was in denial about the number of gay priests.
Earlier this year the former head of state criticised Pope Francis who she said was "blind" to improving the role of women in the church.
"There is a blindness here... that leaves so many good, decent, gentlemanly men like Francis still carrying an element, a residual element, of misogyny."
In February she also criticised the Pope for his comments after he defended the rights of parents to smack their children.