Du Plessis is perhaps most remembered for helping lead an interracial coalition to push for reforms to empower black South Africans and lessen government discrimination in the early 1920s, such as by limiting the pass laws.
[1] He was ordained by the Dutch Reformed Church of South Africa, although relations between him and the DRC declined in his later life over his liberal and modernist theological views, culminating in an accusation of heresy and his dismissal as professor at the University of Stellenbosch.
However, du Plessis's work with international Christian missionaries had given him an ecumenical bent, and he did not believe certain passages of the Bible should be taken "literally", particularly creation according to Genesis and the Old Testament.
These heresy charges distracted the minister from his other work, and what would later become apartheid began to set in South Africa's government in the 1930s, which would reverse many of his earlier successes.
After his death, a life sized statue of Johannes was erected in the town of Stellenbosch and positioned a hundred meters down the road facing the seminary gate.