Brian Donnelly was born in Jersey City, New Jersey, and enrolled in the School of Visual Arts in New York specializing in illustration in 1996. His career as a graffiti artist began when he lived in Jersey City. Later, when moving to New York in the 1990s, KAWS began to modify advertising images at bus stops and telephone booths. These redesigned posters were forgotten and could take several months, but when the popularity of KAWS skyrocketed, the posters were intensely sought after.

In the late 1990s, KAWS began designing and producing limited editions of toys made with vinyl. More toys and clothing was created for Original Fake, a then emerging store in collaboration with Medicom Toy, in the Aoyama district, Tokyo. KAWS also participated in other commercial collaborations with music producer Nigo for clothing brand A Bathing Ape, with Jun Takahashi for Undercover and with Michael Neumann for Kung Faux. He was also invited to design snowboards for Burton and shoes for Nike and Vans. In August 2010 he created a limited edition of bottles for Mexican beer Dos Equis.

The acrylic paintings and sculptures made by KAWS contain many recurring images, all with the purpose of being universally understood, regardless of language or culture. One of the first series of KAWS, Package Paintings, was made in the year 2000. Another series, entitled The Kimpsons, showed an altered version of the popular television series The Simpsons. Other popular icons that have been modified by KAWS are Mickey Mouse, the Michelin Man, the Smurfs and SpongeBob.