His parents were Mary Jane Thomas and Reverend William Humphrey Barnes, and he was the second of four brothers.

While at Dunbar, one of his teachers was Jane Eleanor Datcher, who was the first African-American woman to earn an advanced degree from Cornell University.

[4] Following graduation, Barnes was appointed a chemistry instructor at Amherst, making him the first African American member of the faculty there.

[6] In 1922, Barnes was hired at Howard University in Washington, D.C., as a faculty member in the chemistry department.

While at Howard, one of his doctoral students was Harold Delaney, who later went on to work as a chemist on the Manhattan Project.

[8] Over the course of his career there, he advanced the chemistry department from a masters-only program to granting doctoral degrees.

[9] Barnes, along with fellow professors Roscoe McKinney, Sterling Brown, and Mercer Cook, charted Phi Beta Kappa at Howard, and all were also members of the Gamma chapter of Omega Psi Phi, which was founded at Howard in 1911.