William J. Pennock joined the Communist Party in 1936 while a student at the University of Washington. From 1936-1938, he worked for the Washington Commonwealth Federation, first as a secretary and then as an elected member of the WCF executive committee. He left the WCF in December of 1938 to organize neighborhood locals for the newly incorporated Washington Old Age Pension Union, which, became the first government-funded pension program for senior citizens in the United States. Pennock was elected to the State Legislature in 1938, running as a Democrat. He would be reelected in 1940, 1942, and again 1944. From the state legislature Pennock continued to champion the Washington Pension Union Pennock was one of the seven Northwest Commuinist Party leaders arrested and tried for conspiracy under the Smith Act. During the trial he died of an overdose of pills which was officially ruled a suicide.

His wife, Louise Hastert, was an actress whose career included theater and work at the Seattle Repertory Playhouse which was a progressive community theater which was eventually targeted by the Washington State Committee on Un-American Activities