Convicted wife killer Gerard Baden-Clay has turned to God in prison.

In the lead-up to his trial, Baden-Clay wrote a letter to friends that said he felt fortunate to have been introduced to a prison pastor.

The High Court has been told the Queensland Court of Appeal erred in its decision to downgrade Gerard Baden-Clay's murder conviction.

"He visits me regularly and has been helping me with general pastoral care as well as guiding my Bible study and faith journey," the letter, leaked to the News Corp said.

The Court of Appeal on Friday heard the former real estate agent's appeal against his conviction for killing his wife Allison.

A judgment is expected within three months.

AAP