The TV presenter has sold two-part series Renèe and Flo to publisher Hot Key Books.
Porter said: "I've been talking about Renèe and Flo for nearly a year now, discussing the complexities of female friendships.
"I have a lot to say on the matter. I can't wait to see these books published!"
She added: "It is so exciting to be a part of Hot Key Books. The team is so full of energy and I couldn't be happier to have my first piece of fiction published by them."
Aimed at readers aged over 12, the epic girls' adventure books explore the bond between female friends and are based on Porter's own experiences growing up in Guernsey.
Porter's partner, IT Crowd and Bridesmaids star Chris O'Dowd, proposed to her in Guernsey on Boxing Day last year.