Eugene Dennis (August 10 1905 - January 31 1961) was a long time leader of the Communist Party USA and union organizer. He was born Francis Xavier Waldron in Seattle but adopted the pseudonym of Eugene Dennis in the 1930s.

He worked in various jobs and was active in the Industrial Workers of the World (IWW) prior to joining the Communist Party in 1926 and was active in California as a union organizer.

He fled to the Soviet Union in 1929 to evade criminal charges for his political activities. He returned to the United States in 1935 and assumed his pseudonym. He became general secretary of the party after the expulsion of Earl Browder and was a staunch supporter of the Moscow line.

On July 20, 1948, Dennis and eleven other party leaders, including Party Chairman William Z. Foster were arrested and charged under the Alien Registration Act. Foster was not prosecuted due to ill health.

As Dennis and his co-accused had never openly called for the violent overthrow of the United States government, the prosecution depended on passages from the works of Karl Marx and Vladimir Lenin and on the testimony of former members of the party who claimed that Dennis and others had privately advocated the use of violence.

After a nine month trial and the imprisonment of the defense lawyers for contempt of court, Dennis and his co-defendants were found guilty and sentenced to five years imprisonment. They appealed to the Supreme Court of the United States which ruled against the defendants on June 4 1951 by a margin of 6 to 2.

Dennis remained general secretary until 1959, when he succeeded Foster as party chairman, and held that position until his death in 1961.