Marshall uses collage, painting, photography, video, and installations to reflect on black identity in the United States. He mainly uses large-scale paintings depicting black figures historically excluded from the artistic canon. He has explored issues of race and history through imagery ranging from abstraction to comics. His paintings also illustrate the effects of the civil rights movement on domestic life, in addition to playing with elements of popular culture.

Marshall fights against the stereotypical representations of black people in society by reasserting their place within the canon of Western painting. “You can’t be born in Birmingham, Alabama, in 1955 and grow up in South Central [Los Angeles] near the Black Panthers headquarters,” Marshall has said, “and not feel like you’ve got some kind of social responsibility. You can’t move to Watts in 1963 and not speak about it. That determined a lot of where my work was going to go…”

In April 2016, Marshall's retrospective Mastry debuted at the Museum of Contemporary Art in Chicago as the largest retrospective to date of Marshall's art, which spanned the artist's 35-year career and included nearly 80 original pieces. The retrospective exhibition then traveled to the Metropolitan Museum of Art in New York City, before closing at the Museum of Contemporary Art in Los Angeles a year later. People can also experience the exhibition through virtual reality since last November.