Before his appointment to the bench in 1991, Johnson was an attorney for 25 years, specializing in drug enforcement and the prosecution of narcotics cases.

As Special Narcotics Prosecutor for the City of New York, he supervised assistant district attorneys and investigators responsible for the preparation and prosecution of more than 7,000 criminal cases.

He was the executive director of the Civilian Complaint Review Board of the New York City Police Department from 1970 to 1974.

He was confirmed by the United States Senate on June 27, 1991, and received commission on July 2, 1991.

[2] Johnson was a founding member of NOBLE, a national organization of African American police officers.