The Archbishop of Canterbury voiced his opposition to gay couples adopting and advised Michael Portillo about the "homosexual experiences" he had as a student, according to an upcoming biography.
The first biography about John Welby, the new leader of the Church of England, will also reveal that he repeatedly asked himself whether Jesus would approve the "big buildings" and clerical dresses of the Anglican faith.
The book will look at the rise of Welby from former oil executive and priest at small parish to the leader of the church.
Some of the more outspoken revelations in the book are taken from letters to his parish. In one letter in 1999, Welby criticised Church of England charity The Children's Society's decision to lift its ban on allowing children to be placed into care with same-sex couples.
Following this decision, Welby said his parish will have to "review its decision to support them" and urged the charity to rethink.
In the same article Rev Welby, as he then was, discussed how the former Tory Cabinet minister Michael Portillo admitted to him of "homosexual experiences" as a student.
While Welby told Portillo this would not have an effect on his political career, he advised the MP that: "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," according to the Daily Telegraph.
Another letter showed his opposition to the amount of money being spent on constructing the Millennium Dome, adding he believes Jesus "would not have been very keen on big buildings at all."
Welby is due to be formally installed in Canterbury later this month.