Gregory Joseph Gillespie (1936 – 2000) was born in Roselle Park, New Jersey. After graduating from high school, he became a nondegree student at Cooper Union in New York. In 1959 he married Frances Cohen (1939–1998), who was also an artist, and the following year they moved to San Francisco where Gillespie studied at the San Francisco Art Institute.
In 1962 he received the first of two Fulbright-Hays grants, for travel to Italy to study the work of Masaccio. He lived and worked in Florence for two years, and in Rome for six years, studying the works of such Renaissance masters as Carpaccio, Mantegna, and Carlo Crivelli, who was a particular favorite of Gillespie. During this time he was awarded three Chester Dale Fellowships and a Louis Comfort Tiffany grant. In 1971 he was elected into the National Academy of Design as an Associate member, and became a full Academician in 1994.
He had his first solo show in 1966, at the Forum Gallery in New York. In 1970 he returned to the United States, where he settled in Williamsburg, Massachusetts. He exhibited in several Whitney Biennials, and in 1977 the Hirshhorn Museum organized a touring retrospective of his work.
Gillespie became known for meticulously painted figurative paintings, landscapes, and self portraits, often with a fantastical element. Many of his early works were made by painting over photographs cut from newspapers or magazines, transforming the scenes through photographic collage and by adding imaginary elements. In his later work he abandoned his early fascination with creating hyper-realized realistic imagery, instead focusing on a looser and more expressive style. He often combined media in an unorthodox way to create shrine-like assemblages.