His parents, Louis Klonsky and Bella or Becky (Beile Berezowska), were poor religious Jews who had emigrated from the Russian Empire.

They were convicted in 1954 of violating the Smith Act, which outlawed "teaching or advocating the overthrow of the American government by force".

[4] After 1958, Klonsky lived in California, where he ran a bookstore near UCLA and where he remained active in organizing workers in the film industry.

[5] His son, Michael Klonsky, also became active in politics, becoming a national secretary of the Students for a Democratic Society and later leader of the Communist Party (Marxist-Leninist).

Robert Klonsky supported the jailed professor Angela Davis, demonstrated against the Vietnam War and had a few acting parts in movies.