His NEGRO SLAVE REVOLTS IN THE UNITED STATES 1526-1860 (1939), includes a table of documented slave revolts by year and state. His doctoral dissertation, American Negro Slave Revolts, was published in 1943.
Doing research in Southern libraries and archives, he uncovered 250 similar episodes. It remains a landmark and a classic work in the study of Southern history and slavery.
Aptheker challenged racist writings, most notably those of Georgia-born historian Ulrich Bonnell Phillips. The latter had characterized enslaved African Americans as child-like, inferior, and uncivilized; argued that slavery was a benign institution; and defended the preservation of the Southern plantation system. Such works had been common in the field before Aptheker's scholarship revealed a much more nuanced society, in which African Americans acted from agency.
Considering himself a protégé of W. E. B. Du Bois, Aptheker long emphasized his mentor's social science scholarship and life-long struggle for African Americans to achieve equality.
In his work as a historian, he compiled a documentary history of African Americans in the United States, a monumental collection which he started publishing in 1951. It eventually resulted in seven volumes of primary documents, a tremendous resource for African-American studies.