After receiving his law degree from the University of Chicago, Raymon T. Johnson accepted a position to teach at W&L for the 1925-1926 academic year. He left after that year to establish the law firm of Porter and Johnson in Louisville, Kentucky. The practice did not thrive, however, and Johnson accepted an invitation to return to W&L in the fall of 1927. He became one of the "Old Guard" professors and remained at the law school until his death.

Early in his teaching career, Johnson taught Torts, Municipal Corporations, Constitutional Law, Partnership, Insurance, Quasi Contracts, Administrative Law, Suretyship, Public Utilities, Bankruptcy, and Sales. His specialties, though, were Conflicts of Laws, Criminal Law and Procedure, and Domestic Relations. After World War II he added Trade Regulations to his repertoire.