Andrew Wallace has described his shock at finding out his daughter was gay.
The Queensland Liberal backbencher is a practising Catholic, goes to church most Sundays, and joined a monastery in his late teens.
"About three years ago our daughter told my wife and I that she was attracted to women - that she had a girlfriend," Mr Wallace told parliament on Tuesday, during debate on legalising same-sex marriage.
"My wife and I were shocked. Probably more me than my wife. I didn't know what to say."
For most of his adult life, Mr Wallace had shared the Catholic view that marriage is between a man and a woman.
"Homosexuality went against what I had been taught to believe for many years. How could this be happening? How could this be happening to me, to our family?", he posited.
His daughter Caroline struggled with mental illness and eating disorders throughout her teenage years.
Caroline had boyfriends growing up, but told her father "it never felt quite right" and she felt she could not tell her parents because she thought they would not approve.
"She said she had always secretly been attracted to women and I'm sure this internal conflict would have, in some part, at least exacerbated her mental state," Mr Wallace told parliament.
Mr Wallace said his daughter was now in a much healthier and happier place.
"She has a terrific job and a wonderful partner who our family love very much."
Caroline offered her father a poignant parallel during their initial discussion.
"She said, 'Dad, in the years to come, my generation will look back and judge your generation about how you deal with the issue of homosexuality'," he told MPs.
"In the same way your generation considered your parents' generation in the way they dealt with our indigenous people."
Mr Wallace will support same-sex marriage but wants to see greater religious protections in the bill.
"In this country, we do not discriminate against someone because of the colour of their skin, their religion, nor their place of birth," he said.
"In law, we are all created equally. And so we ought not in law discriminate against a person by virtue of their sexual preference."