Steig was born in Brooklyn, New York, in 1907, and grew up in the Bronx. His parents were Polish-Jewish immigrants from Lemberg, Austria-Hungary; both socialists. His father, Joseph Steig,[4] was a house painter, and his mother, Laura Ebel Steig, was a seamstress who encouraged his artistic leanings. As a child, Steig dabbled in painting and was an avid reader of literature. Among other works, he was said to have been especially fascinated by Pinocchio. In addition to his artistic endeavors, Steig also did well at athletics, being a member of the collegiate All-American water polo team. He graduated from Townsend Harris High School at 15 but never completed college, though Steig attended three, spending two years at City College of New York, three years at the National Academy of Design and a mere five days at the Yale School of Art before dropping out of each one.[5]

Hailed as the "King of Cartoons",[6] Steig began drawing illustrations and cartoons for The New Yorker in 1930, producing more than 2,600 drawings and 117 covers for the magazine. One of his cartoon characters, Poor Pitiful Pearl, was made into a popular line of dolls starting in 1956.[7]

Steig began writing children's books when he was 61.[8] In 1968, Steig published his first children's book. He excelled here as well, and his third book, Sylvester and the Magic Pebble (1969), won the Caldecott Medal.[9] Steig went on to write more than 30 children's books, including the Doctor De Soto series, and he continued to write into his nineties. Among Steig's other well-known works, the picture book Shrek! (1990) formed the basis for the DreamWorks Animation film Shrek (2001). After the release of Shrek 2 in 2004, Steig became the first sole-creator of an animated movie franchise that went on to generate over $1 billion from theatrical and ancillary markets after only one sequel.[10]

When asked his opinion about the movie based on his picture book Shrek, William Steig responded: “It’s vulgar, it’s disgusting — and I loved it.”[11]

In 1984, Steig's film adaptation of Doctor De Soto, directed by Michael Sporn, was nominated for the Academy Award for Best Animated Short Film. That same year, Steig received the CINE Golden Eagle Award in Education[12] for the film adaptation of this book.

Steig married four times and had three children. From 1936 to 1949, Steig was married to educator and artist Elizabeth Mead Steig (1909–83, sister of anthropologist Margaret Mead),[13] from whom he was later divorced. For a time, Steig lived at 75½ Bedford Street, purported to be the narrowest house in Manhattan.[14] Steig's first marriage also made him a brother-in-law of Leo Rosten[13] and an uncle of Mary Catherine Bateson.[15] Steig and Mead were the parents of jazz flutist Jeremy Steig (playing the Pied Piper in Shrek Forever After)[16] and a daughter, Lucinda. He married second wife Kari Homestead in 1950, and they had a daughter, Margit Laura (now professionally known as Maggie Steig).[17] After their divorce, he was married to Stephanie Healey from 1964 to 1966. His final marriage, to Jeanne Doron in 1968, endured for the rest of his life.

Steig's brother Irwin was a journalist and painter, for whom William illustrated two books on poker strategy. His brother Henry was a jeweler and a writer who played the saxophone and painted. And his brother Arthur was a writer and poet, who, according to Steig, read The Nation in the cradle, was telepathic and "drew as well as Picasso or Matisse".[18]

Steig died of natural causes in Boston, Massachusetts, on October 3, 2003, at the age of 95.[19] Shrek 2, which was released seven months after his death, was dedicated to his memory.[4]