He served in the United States Army Corps of Engineers from 1943 to 1946 where he attained the rank of sergeant.

In 1957 he became the first African-American to be appointed Assistant United States Attorney for the District of Maryland, serving in that capacity for five years.

[2][3] In 1962, he was appointed Judge of the old People's Court, where he served for a brief time before losing an election for the position.

Ground for this new courthouse was broken in 2001, and it is named in honor of the late Judge John R. Hargrove Sr., who died April 1, 1997.

[5] His son John Raymond Hargrove Jr. was appointed to the District Court of Maryland for Baltimore City by Governor Parris Glendening in 1998.