After his admission to the bar on March 6, 1947, he was the city of Portsmouth's assistant solicitor until 1951, when he was elected Scioto County Prosecuting Attorney. He served one four-year term. In 1961, he was elected to Congress and served twenty years there. He was succeeded by Bob McEwen, who had managed two of his re-election campaigns.
After his retirement from Congress, he was a consultant in Washington, D.C., from 1981 to 1986, when he returned to Portsmouth and resumed his law practice. [citation needed]
Harsha married Rosemary L. Spellerberg on June 24, 1946.[3] Their son, William H. Harsha III, is a judge of the Ohio Court of Appeals for the Fourth Appellate District.