Throughout his career, Johnson looked to support minority scientists and engineers. He was involved with outreach and education programmes for minority students, and supervised several doctoral researchers. In the early 1970s he helped to arrange the first meeting of African-American physicists. The meeting, which was hosted at Fisk University, honoured Donald Anderson Edwards, John Hunter and Halston Eagleson. In 1977 Johnson was one of the founding members of the National Society of Black Physicists (NSBP). He helped to draft the constitution and went on to serve as President. His legacy is recognised by the American Institute of Physics and NSBP, who, in 2021, established the Joseph A. Johnson III Award for Excellence. In 1988 he worked with Abdus Salam to host a meeting for African and African-American physicists at the International Centre for Theoretical Physics. A direct outcome of the meeting was the formation of the Edward Bouchet Abdus Salam Institute, which supports African doctoral researchers in attending graduate school in the United States. In 2003 he helped to establish the African Laser Centre, a network of laser laboratories across Africa that provides fellowships for graduate students.