James Turnbull was born in Saint Louis, Missouri in 1909. He received a scholarship to attend the University of Missouri in 1928, where he studied journalism. During Christmas vacation in 1929 he suffered an accident that required two months of recuperation. Hopelessly behind in his studies, he entered the School of Fine Arts in Saint Louis, where he spent three years. A year of study at the Pennsylvania Academy of the Fine Arts completed his education.
Returning to Saint Louis, Turnbull promptly began to work in earnest. He joined the Artists Union. Missouri did not have a WPA Federal Art Project at that time, so in 1937, at the age of twenty-eight, Turnbull led a delegation of Artists Union members to Washington, DC where he successfully lobbied for WPA support in the state. Turnbull was named director of the Missouri WPA project, but resigned after only four months, finding his duties left him no time to paint.
Turnbull's choice of subject matter, which was mainly concerned with farmers and life in small towns, was influenced by other Midwest artists, such as Thomas Hart Benton, Grant Wood, and John Steuart Curry. Turnbull's style, however, is more straightforward, and he shares few of their mannerisms. In many of his paintings, the subject occupies a limited pictorial space and thus appears to the viewer with a sense of immediacy.
Soon after Turnbull resigned his administrative post with the WPA, he won a contest to paint a mural in the Post Office in Purcell, Oklahoma. This led to other commissions, the largest of which was for a series of murals, measuring altogether almost three hundred feet in width, to be painted in collaboration with Joe Jones for the 905 Stores, Inc., in Saint Louis. It had previously been assumed that Jones executed the major portion of the murals, but close examination reveals that, on the contrary, the paintings were on the whole completed by Turnbull.
Turnbull spent World War II as a correspondent for Life magazine and Abbott Laboratories. He spent most of his time in the Caribbean. After the war, he and his wife settled in Woodstock, New York.