The Fox And The Star by Coralie Bickford-Smith, a designer at Penguin Books, was named Waterstones Book of the Year.
The winning book was described as one of “great physical beauty and timeless quality” which appeals to both children and adults.
It had stiff competition on the shortlist from literary heavyweight Lee, whose novel Go Set A Watchman — a follow-up to To Kill A Mockingbird, caused a sensation when it came out earlier this year.
Ms Bickford-Smith said: “I am incredibly touched and honoured that The Fox And The Star has been voted Waterstones Book of the Year 2015.
“I am especially thrilled that the Waterstones booksellers have chosen a book that hopefully speaks to children and adults alike. The Fox And The Star was the result of a very personal journey, so for it to be recognised in this way means a lot to me.”
Other books on the shortlist were The Girl On The Train by Paula Hawkins, SPQR by Mary Beard and The Shepherd’s Life by James Rebanks.