Awarded his doctorate at Brandeis in 1998 for a dissertation supervised by Jacqueline Jones, Kelly has published widely on race and class in the nineteenth and twentieth-century United States, including an award-winning study of working-class interracialism in the Birmingham district (Alabama) coal mines.
It argued that the re-subordination of black labor that followed the defeat of Reconstruction was a key component of the New South modernization project: progress and reaction went hand-in-hand.
In a series of articles published after the Alabama study, Kelly attempted to follow up on this latter theme, charting the emergence of intra-racial tensions across the Jim Crow South, including in his "Sentinels for New South Industry," published in Time Longer than Rope (2003), in a chapter in Eric Arnesen's The Black Worker: Race and Labor Activism since Emancipation (2007) and in "No Easy Way Through: Race Leadership and Black Workers at the Nadir" (2010).
His current project is an extended monograph on African American labor and political mobilization in black-majority Reconstruction South Carolina, under contract with Verso.
He has published a number of articles on the controversy about Irish involvement in the transatlantic slave trade, including a two-part series in Rebel, and a Platform piece on the subject in History Ireland.