The former hell-raiser, now 54, said on her website she had come a long way from the atheism of her youth in communist East Germany, where she rebelled against the regime and launched her music career.
"She has more to tell than the usual mixture of sex, drugs and rock'n'roll," a blurb from her publisher Droemer Knaur about the book "Confessions: My Path to God" posted on her website said.
"Nina tells how she, at an early age in an atheist environment, came upon a forbidden but fascinating being named God. She takes the reader with her on a wild road movie in which she has demonic experiences in an Indian ashram.
"On the way, she looked love, drugs and death in the eye. But above all, she encountered God."
The book is to be released in March. Hagen told Thursday's Bild newspaper that she had been baptised in August and that she wanted to share with readers the joy of finding Jesus. "The baptism saved my life," she said. "I was in a bad way before that."
Hagen defected to West Germany in 1976 following the expulsion of her stepfather, activist singer-songwriter Wolf Biermann. From there, she landed in London just as punk erupted on the music scene.
Renowned for her raucous, uninhibited stage show, she courted controversy with stunts such as feigning masturbation on a television chat show.
In recent years, she has done voice-overs for film, released an album of swing music and integrated Christian songs into her live act.