The Smith Act trials of Communist Party leaders were a series of federal prosecutions conducted from 1949 to 1958 in which leaders of the Communist Party of the United States (CPUSA) were accused of violating the Smith Act, a statute which imposed penalties on those who advocated violent overthrow of the government. The prosecution argued that the CPUSA's policies promoted violent revolution; the defendants countered that they advocated a peaceful transition to socialism, and that the First Amendment's guarantee of freedom of speech and of association protected their membership of a political party. The trials led to the US Supreme Court decisions Dennis v. United States (1951) and Yates v. United States (1957).
The first trial, held in New York in 1949, was one of the lengthiest trials in American history. Large numbers of supporters of the defendants protested outside the courthouse on a daily basis. The trial featured twice on the cover of Time magazine. The defense frequently antagonized the judge and prosecution, and five defendants were jailed for contempt of court because they disrupted the proceedings. The prosecution's case relied on undercover informants who described the goals of the CPUSA, interpreted communist texts, and testified that they believed the CPUSA advocated the violent overthrow of the US government.
While the first trial was under way, events outside the courtroom influenced public perception of communism: the Soviet Union tested its first nuclear weapon, and communists prevailed in the Chinese Civil War. Public opinion was overwhelmingly against the defendants. After a 10 month trial the jury found all 11 defendants guilty and the judge sentenced them to terms of up to five years in federal prison, further sentencing all five defense attorneys to imprisonment for contempt of court. Two of the attorneys were subsequently disbarred.
After the first trial, the prosecutors – encouraged by their success – prosecuted over 100 further CPUSA officers for violating the Smith Act. Some were tried solely because they were members of the Party. Many of these defendants had difficulty finding attorneys to represent them. The trials decimated the leadership of the CPUSA. In 1957, eight years after the first trial, the US Supreme Court's Yates decision brought an end to similar prosecutions, holding that defendants could be prosecuted only for their actions, not for their beliefs.