On April 3, 1939, Mr. District Attorney launched his radio crusade for law and order - a campaign that would last on the air until 1952. 

The series was created by Ed Byron, a former law student who collaborated with Gang Busters creator Phillips H. Lord. Loosely inspired by New York Governor (and future legendary losing presidential candidate) Thomas E. Dewey fight against racketeers, the series chronicled the efforts of the unnamed prosecutor as he battled criminals.

For most of the run, the DA was played by Jay Jostyn, but Dwight Weist and Raymond Edward Johnson played him early in the run. Jostyn's portrayal of the upstanding district attorney was so convincing, that, according to a 1952 Radio-TV Mirror article, “He is so generally believed to be a real life lawyer that he frequently receives mail from listeners inviting him to move to certain cities where they feel crimes are going unsolved.” Vicki Vola portrayed the DA's loyal secretary Miss Miller, and Len Doyle played the DA's chief investigator Len Harrington. The trio formed one of radio's best crime-solving units, tracking down crooks played by some of the best actors in East Coast radio.

The show spawned a pair of TV shows, one featuring the radio cast and the second starring David Brian as the DA. By that time, the prosecutor had been given the name Paul Garrett, and Brian would reprise the role for a final run of syndicated radio episodes.