Ardizzone was born at Haiphong, Tonkin, French Indo-China, where his Algerian-born Italian father was on overseas government service. Ardizzone's English mother returned to England with her three eldest children in 1905. The children were brought up in Suffolk, largely by their maternal grandmother, whilst their mother returned to join her husband in the Far East. Ardizzone was educated first at Ipswich School and then at Clayesmore School - where he was encouraged by his art teacher. (see: an Autobiographical Fragment (London 1970))
He worked as an official war artist in World War II: his early experiences between Arras and Boulogne are illustrated and described in his book Baggage to the Enemy (London 1941). An extensive collection of his war pictures, as well as his wartime diaries, can be seen at The Imperial War Museum.
His best known work is the Tim series, featuring the maritime adventures of the eponymous young hero. The first book, Little Tim and the Brave Sea Captain, was published in 1936. The most famous of the books, Tim All Alone, won the British Library Association's Kate Greenaway Medal for illustration in 1956. The series is often thought to have ended in 1972 with Tim's Last Voyage but that was, in fact, followed in 1977 by Ships Cook Ginger. His Sarah and Simon and No Red Paint was issued in an edition by Doubleday in 1966.
As well as writing and illustrating his own books, Ardizzone also illustrated books written by others, including the novels of Anthony Trollope. His 1939 characterization of H.E. Bates's My Uncle Silas was inimitable. Among his happiest collaborations was that with Eleanor Farjeon, especially The Little Bookroom.
He illustrated the Nurse Matilda series of children's books written by his cousin, author Christianna Brand. Both cousins heard the stories from the same grandmother - who had, in her turn, heard them from her father. He also famously illustrated A Ring of Bells, John Betjeman's abridged version for children of his Summoned by Bells autobiographical poem. He worked on C. Day Lewis's children's novel The Otterbury Incident, as well as some novels by the American author Eleanor Estes, including The Alley, Miranda the Great, Pinky Pye, The Tunnel of Hugsy Goode and The Witch Family.He is also particularly noted for having not just illustrated the covers and contents of books but inking the title text and author's name in his own hand, giving the books a distinctive look on shelves. An example is Clive King's Stig of the Dump.
Ardizzone illustrated a series of books for young children by Graham Greene including The Little Fire Engine, The Little Horse Bus,The Little Train and The Little Steamroller. He also illustrated a re-telling of the Don Quixote story for children by James Reeves.
Ardizzone also illustrated several telegrams for the Post Office in the 1950s and 1960s, many of which are considered collector's items.
His style is naturalistic but subdued, featuring gentle lines and delicate watercolours, but with great attention to particular details.
He was elected to the Royal Academy of Arts in 1970, and appointed CBE in 1971. The British Library published an illustrated bibliography of his works in 2003.