Bob Davey was told about St Mary's in Houghton on the Hill, Norfolk, by his late wife Gloria, who discovered it during a walk.
At the start, the church tower was completely covered in leaves and there were piles of rubbish outside the door. The church had no roof, doors or windows. It had also been hit by a German bomb during World War II.
Satanists had begun using the derelict church before Bob started restoring it. He claims they threatened to kill him when he first started work.
In the beginning, he had to guard the church at night to stop them returning and enlisted the Territorial Army to help guard.
Bob told Premier: "It was a sacred site which was being abused, and the only way to do it is to sort it out and bring it back to life.
"Life's like this: you're presented with a situation. You can either ignore and walk away, or you can take it on, and I took it on."
"I've got a lot out of it you know. Buckingham Palace garden party, all these visitors, something to spend my retirement on...
"If you want a good retirement, take on a ruined church. You'll never look back."
When he was fixing the wall hit by a German bomb, Bob discovered wall paintings of the Holy Trinity and the Last Judgement, which are thought to date back almost 1,000 years. They had been covered in whitewash plaster.
They are believed to be the oldest wall paintings in Britain, and have helped make the church an international tourist attraction.
Bob is currently raising the £50,000 needed for specialists to remove the plaster, which still covers a lot of the artwork.
Prince Charles has visited the church several times, and Bob has received an MBE for his efforts.
The church now has protected status, and people from different denominations worship there regularly.