Dewulf works mainly on slavery and African-American culture in Dutch Brazil, New Netherland and New York City, most notably the legacy of Pinkster and Sojourner Truth in his book The Pinkster King and the King of Kongo: The Forgotten History of America's Dutch-Owned Slaves (2017), and in Louisiana, most notably the origins of the Mardi Gras Indians in his book From the Kingdom of Kongo to Congo Square: Kongo Dances and the Origins of the Mardi Gras Indians (2017).

Together with Olf Praamstra and Michiel van Kempen, he edited the book Shifting the Compass (2013); with Luc Renders, he published an anthology of Flemish literature on the Congo (2020).

In Brasilien hit Brüchen (2007), he also focused on other Swiss writers in Brazil, including Johann Jakob von Tschudi, Louis Agassiz, Blaise Cendrars, and Richard Katz.

In 2015, he was distinguished with the Louisiana History President's Memorial Award and both in 2015 and 1016, he received the Clague and Carol Van Slyke Prize.

His 2022 book on the history of Black Christianity was awarded the 2023 John Gilmary Shea Prize by the American Catholic Historical Association.