The TV presenter, who is mum to Harry, six, Belle, four, and Chester, one, with husband Dan Baldwin, teamed up with publisher Harper Thorsons to create the "practical parenting guide from a mum you can trust".
"Excited to announce my new book 'Truly Happy Baby'. All the best bits I've learnt being a mum," Willoughby said when announcing the release on Twitter.
Willoughby has drawn from her own experiences to offer guidance and tips on ways "to find calmness throughout the chaos".
According to Amazon, the book will encourage mums during their first twelve months of parenthood to trust their natural instincts and to care for their children in their own way.
"Whilst Willoughby acknowledges the benefits a good routine can bring, she wants you to listen to your mummy intuition to know what’s best for you and your baby," the description of the book reads.
"Packed with achievable, practical advice and full of the ideas, techniques and tips that helped her throughout the first year of her babies’ lives, Holly will hold your hand through the exhausting bits and share in the brilliant bits, too.
"This is the friendly and accessible approach to parenting that will see you through the sleepless nights, concerns and worries, to all the magical first moments and more."
The book will have chapters on 'feeding', 'sleeping', 'lifestyle' and 'looking after you'.
It is currently available to pre-order and will be released on 16 June 2016.
Parents were excited by the announcement on Twitter, with many replying within minutes of finding out.
This isn't the first time Willoughby has entered the publishing world.
In 2010, the mum-of-three released non-fiction book "The Best Friends' Guide to Life" with her pal Fearne Cotton.
From 2013-2014, Willoughby and her sister Kelly Willoughby released six books in the "School for Stars" children's series, which follows twins Maria and Molly Fitzfoster and Pippa Burrows on a quest to achieve their dreams of super stardom.
Truly Happy Baby: A practical parenting guide from a mum you can trust will be £16.99 hardcover or £10.99 on Kindle.