American painter and sculptor who was a leading exponent of the hard-edge style, in which abstract contours are sharply and precisely defined.

Kelly studied at the Boston Museum of Fine Arts School (1946–48) and at the Académie des Beaux-Arts (1948–49) in Paris. He had his first one-man show in Paris in 1951 and returned to the United States in 1954. He rejected illusionism in his paintings, which typically consist of adjacent rectangular panels of flat, uninflected primary colours. Kelly used the clean geometric lines of his paintings (e.g., “Red Blue Green,” 1963) in his painted, cut-out metal sheet sculpture (e.g., “Gate,” 1959). He was commissioned to do sculptures for the Transportation Building in Philadelphia (1957) and the New York State Pavilion at the New York World's Fair (1964–65).