Hillary Clinton's Catholic running mate Tim Kaine believes his Church is on the road to dropping its opposition to gay marriage.

Senator Kaine told the pro-LGBT Human Rights Campaign that he changed his own mind about gay marriage in 2005 and believes the Catholic Church will do the same.

Kaine quoted Pope Francis, whose remark: "Who am I to judge?" raised hopes in the LGBT community that he was heading in a more liberal direction. Subsequent statements however made it clear that while he opposes homophobia, there is no plan to relax any aspect of the Church's teaching on marriage.

In a new book earlier this year, Pope Francis clarified what he meant by his comment, made early in his papacy in 2013 to journalists on the papal plane. The Pope explained: "On that occasion I said this: If a person is gay and seeks out the Lord and is willing, who am I to judge that person? I was paraphrasing by heart the Catechism of the Catholic Church where it says that these people should be treated with delicacy and not be marginalised."

People should not be defined only by their sexual tendencies, he added. "Let us not forget that God loves all his creatures and we are destined to receive his infinite love. I prefer that homosexuals come to confession, that they stay close to the Lord, and that we pray all together."

Kaine, former Governor of Virginia, is an advocate for gay marriage and co-sponsor of the Equality Act. He has repeatedly supported anti-discrimination legislation. 

He was speaking at the Human Rights Campaign's annual dinner in Washington.

He had once opposed gay marriage because he believed marriage was different in the context of the LGBT battles for equal rights. 

He changed his mind and said he believed the Church was on course to change its mind on the issue.

"I think it's going to change because my church also teaches me about a creator who, in the first chapter of Genesis, surveyed the entire world, including mankind, and said, 'It is very good'."

He said he wanted to add to the Pope's comments. "I want to add: Who am I to challenge God for the beautiful diversity of the human family? I think we're supposed to celebrate it, not challenge it."

Gay marriage was legalised in the US in summer of 2015.