Bennett College in Greensboro, North Carolina, will offer Aaron Douglas's 1931 painting Harriet Tubman at Sotheby's New York on 18 November, estimated at $2.5 million to $3.5 million. The figure is the highest ever placed on a work by Douglas, whose previous auction record stands at just $600,000, set in 2008 for a far smaller painting. Six feet wide, the Tubman canvas is larger than any of the artist's works previously sold at auction, and it will go on public view at Sotheby's headquarters from 7 November, carrying a house guarantee.

The seller is one of only two historically Black women's colleges in the United States. Its acting president said the decision followed more than two years of deliberation, and that proceeds will support women's health equity, including expanding a Women's Health Initiative launched in January to address disparities in care. The painting was commissioned in the 1930s by Chicago philanthropist Alfred K. Stern for a college dining hall, and for the past two decades it has hung at the North Carolina Museum of Art, after the college, which has no museum, concluded it could not care for it.

Douglas, a Kansas-born artist who moved to Harlem in the 1920s, became one of the defining visual voices of the Harlem Renaissance, building his imagery from flattened figures, bold geometry and African motifs. The Tubman painting shows its subject on raised ground, breaking a chain as onlookers gather, among them a man farming his own land and a young woman reading. Its composition recalls Delacroix's Liberty Leading the People, and it predates Douglas's best-known cycle, Aspects of Negro Life, by three years.

Tubman escaped slavery in 1849 and returned south some thirteen times to lead about seventy enslaved people to freedom, later serving the Union Army as a scout and spy and campaigning for women's suffrage. Sotheby's contemporary art chief noted that major Douglas paintings almost never reach auction, with museums acquiring important examples privately in recent years. With a work of this scale and subject now on offer, he expected museums around the world to compete for it.