[3] Barrett's first illustrated book was The King, the Cat and the Fiddle, published in 1983 and written by Yehudi Menuhin and Christopher Hope.
[4] Barrett's work is mainly created using watercolor, gouache, colored pencils, and ink.
[5] For the 1998 book Joan of Arc, she researched 15th-century art and illuminated manuscripts to create a visual style for the story, using motifs inspired by medieval French fabrics.
[6][3] Barrett works in a realistic style with distorted figures, proportions and perspectives.
[3][1] Joanna Carey for The Guardian stated Barrett's illustrations have "a stillness and a quiet atmospheric intensity..."[3] Valerie Coghlan stated in The Oxford Encyclopedia of Children's Literature that Barrett's "slightly elongated figures and faces and distorted perspective are frequently used to heighten tension and impart a sense of mystery.