For 22 years, Anthony Venn-Brown tried to change his sexual orientation through psychiatric treatment, exorcism and conversion therapy.
He turned to God, hoping to become "normal" and later became a preacher in Pentecostal churches such as Hillsong. Everything in his world told him he could not be a gay person.
"It's difficult for people to realise what that internal torment is like," he said.
"You're struggling to conform. But the essence is, you have not changed your orientation.
"When you perceive your orientation to be sick, evil or dysfunctional, that causes intense cognitive dissonance [inconsistent thoughts, beliefs or attitudes]."
This mental state can drive people to "seriously consider taking their own lives".
"And people have over that very issue," he said.
Mr Venn-Brown will on Thursday night give a public lecture at Watt Space Gallery in Newcastle, titled Post-Equality Victory: The Challenges Ahead.
"One of the things that people missed in celebrating the win for the postal survey [for marriage equality] was that nearly 40 per cent of Australians said 'no, you can't have equality'," he said.
"I always say the enemy is ignorance. Sometimes people spend a lot of time attacking other people who have different views."
He said social change and equality often takes decades.
"You can change things with a law, but that doesn't change people's minds or attitudes," he said.
Nevertheless, he believes the visibility of gay people getting married will capture hearts and minds.
As more gay couples have engagement parties and weddings, more people and families will accept gay people having equal rights.
"People will see it's just about love and relationships, not about sex," he said.
Mr Venn-Brown resigned as a minister and ended his 16-year marriage after coming out as a gay man. He later published his autobiography, A Life of Unlearning - A Preacher's Struggle with his Homosexuality, Church and Faith.
He said the church has a problem with gay people because of "a literal interpretation of the Bible".
"They read a religious translation without any historical or cultural context or even looking at the original languages," he said.
Examining these aspects can give insight and a completely different interpretation, he said.
He said this was "very challenging" for the church because "it's attacking the basis of their belief system".
"When you look at some churches, like the Pentecostal church, they've managed to make some huge transitions over the years on divorce, alcohol, fashion, long hair and even having tattoos," he said.
"All these things once were preached against, but not now. Because there's a morality attached to sexual orientation, it's much harder for them to make the transition and look at this in a realistic way."
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