The new Archbishop of Canterbury, Justin Welby, said sex is only for heterosexual marriage and children do best when raised by their married mum and dad.
The comments, reported by the Daily Telegraph, are revealed in a new biography which looks at his parish letters from his early days as a clergyman.
In one letter sent in 1999, he said: “The standards of expected sexual morality are clear.
“Throughout the Bible it is clear that the right place for sex is only within a committed, heterosexual marriage.
“Interestingly, all recent research also shows that the children of such a relationship are likely (not always but often) to be happier and more stable.”
When Justin Welby was appointed as Archbishop of Canterbury in November last year, he confirmed his support for the Church of England’s stance against redefining marriage.
Last Summer, the Church of England attacked the Government’s plans in response to a consultation on the issue.
The Church said redefining marriage could trigger a constitutional crisis and end its 500-year link with the state.
It also said the plans were “divisive” and “essentially ideological”.
It warned that the proposals “would alter the intrinsic nature of marriage as the union of a man and a woman, as enshrined in human institutions throughout history”.