Gilliam was born in Tupelo, Mississippi, in 1933 as the seventh child of eight to a father who worked on the railroad and a homemaking mother, He attended the University of Louisville for both bachelor's and master's degrees, but in 1962 moved to Washington, D. C, , where he lived and had his studio for the rest of his life. He became one of the leading artists of the Washington Color School--a1950s movement that attached great importance to large fields of color.
He was interested in freeing his paintings from the limit of canvases（ 画布） and frames. Instead, in his Drape works of the 1960s, he took unstretched canvases and hung them from ceilings or pinned（ 固定） them in great waterfalls to walls. Each time his work—part painting, part sculpture—was shown in an exhibition, it hung differently, never the same way twice.
In a 2018 Morning Edition profile, Gilliam explained that the intention behind his Drape work was "to develop the idea of movement into shapes"—and that he was inspired by laundry（洗衣店） hanging from a clothesline.
His work is represented in the collections of some of the world's most celebrated museums, including the Metropolitan Museum of Art and the Museum of Modern Art in New York. In 2015, he was awarded the U. S. State Department's Medal of Arts Lifetime Achievement Award.
In the 2018 Morning Edition profile, the then 84-year-old Gilliam said that he felt that he was in his prime, despite health challenges. "I've never felt better in my life. I stopped drinking. I stopped smoking. I live for this period of being in the studio and actually working."
