She was born and raised in Providence, Rhode Island, to an Irish American mother and African American father. Gallagher spent the early years of her life working in an array of jobs: as a commercial fisherman in Alaska, a schooner off the Maine coast, and a celestial navigator in the Caribbean. When she elected to pursue an art degree at the School of the Museum of Fine Arts, Boston, she did so primarily to leave behind her current career in carpentry. After joining Dark Room Collective, a Boston-based group hosting gatherings for Black artists and writers, she began to explore art as a means of expressing her cultural identity.

In her early work from the mid-1990s, following a formative experience at the Skowhegan School of Painting and Sculpture, she used transfer printing techniques in uneven grids and added painted, printed, and stenciled pairs of stylized lips. Those works connected the aesthetics of 1960s Minimalism, biomorphism, and minstrelsy. Since then, Gallagher’s work has combined nonrepresentational, formal concerns with charged figuration—pointing to the artificial division between abstraction and figuration in art. Her paintings and drawings make use of found objects, such as lined penmanship paper, magazine pages, journals, and advertisements, that she transforms through accumulation, erasure, and puncture. The artist has noted the influence of Minimalist artist Agnes Martin and the repetition of modernist writer Gertrude Stein on her practice.

Gallagher attended Oberlin College, Ohio; artist Michael Skop’s private art school Studio 70; the School of the Museum of Fine Arts, Boston; and the Skowhegan School of Painting and Sculpture. She was awarded the American Academy of Arts and Letters Award in 2000 and a Joan Mitchell Fellowship in 1997. The Studio Museum has presented her work in group exhibitions such as Black Belt (2003); The Shadows Took Shape (2013); and Speaking of People: Ebony, Jet and Contemporary Art (2014).