Marc Simont was born in Paris, France, the son of Spanish painter Joseph Simont. He spent his childhood in Paris, Barcelona, and New York City. He became interested in drawing at a very young age. He was often ill as a child, and his education was often interrupted by illness or relocation, and he never finished high school. Nevertheless, he studied art at both the Academie Julien and the Academie Ranson in Paris, although he considered his father to be his most influential art teacher. In 1930, Simont traveled to New York City to attend the New York National School of Design. He settled in the United States permanently in 1935 and resumed study at the National School of Design. In 1938, the year he graduated, one of his instructors hired him and a fellow student to assist in the painting of a series of murals for the Lever Brothers offices in Cambridge, Massachusetts. At around that time, another acquaintance asked him for some drawings for a children’s book manuscript he was sending around to publishers, which is how his work was noticed by the juveniles editor at Dodd, Mead. In the meantime, he was drafted into the Army and sent to the Field Artillery Replacement Training Center at Fort Bragg in Fayetteville, North Carolina for basic training. Upon discovering his artistic skills, he was put to work drawing rifles and other weapons to help with the training on these weapons. During his service he met his future wife, who was working for the USO Travelers Aid, and the two were married. The first children's book he illustrated, Pirate of Chatham Square, was published in 1939. In 1950 he received the Caldecott Honor for his illustrations of Ruth Krauss' The Happy Day. He received the Caldecott Medal in 1957 for his illustrations of Janice May Udry's A Tree is Nice. Over the course of his career, he has illustrated over 100 books.