Peter Barrett was a graphic designer and illustrator by profession. In 1972, he moved into a woodland retreat in England, and has concentrated on finely detailed watercolours of English wildlife and large nature abstracts since then. He is well established as a children's book illustrator, animal artist and a nature artist.

In the late 1970s and early 1980s, Barrett teamed up with Franklin Porcelain. Franklin Porcelain used "Peter Barrett" as a signature brand. Among his crafted and painted products with Franklin Porcelain were a set of thimbles with handpainted images of birds on them, a set of 12 plates with images of the twelve months in the country handpainted on them (called "The Country Years"), a set of plates with handpainted depictions of animals (titled "All Creatures Great and Small") and porcelain figurines of birds. The porcelain figurines of birds were placed upon a porcelain bell. Hence, Bell Birds.

Peter Barrett designed and provided the artwork for a set of United Kingdom postage stamps depicting dogs in 1979. A commemorative first day cover was also brought out.

Peter Barrett's career as an illustrator took off after writing and illustrating a three book series for very young children, along with his wife Susan Barrett. Published by Ward Lock, the books (The circle Sara drew, The square Ben drew, The line Sophie drew) became very popular. Barrett subsequently concentrated on animal art and illustrations, illustrating numerous children's non-fiction books, specializing in dogs, horses and dinosaurs. His illustrations for Birdwatcher's Diary, by Roger Lovegrove, in 1982 drew critical acclaim.

A biographical perspective of his work was published in 1986 by his wife Susan Barrett titled "Travels with a wildlife artist: the living landscape of Greece". Peter Barrett illustrated the book and also contributed to the text. In the decades of the 1980s and 1990s, his stature as an animal artist and children's book illustrator has grown hand in hand. Peter Barrett illustrated reprints and collections of famous animal centric stories and books by Gerald Durrell, Desmond Morris and James Herriot. He illustrated a number of books under the highly popular Little Golden Books label for children. He has also illustrated the 1987 Random House edition of the children's classic The Wind in the Willows, by Kenneth Grahame.

In 2005, he illustrated the 65th Anniversary Edition of Three Little Pigs, published by Ladybird Books.

In 2009, he illustrated Evolution: The Story of Life by Douglas Palmer, published by The University of California Press.