Cohen was elected to the Senate at the 1961 federal election, following a controversial preselection process.
His chief opponent was another prominent Jewish barrister Maurice Ashkanasy, who had the support of the Labor Right faction and had opposed the work of the Jewish Council.
During the campaign an anonymous pamphlet was circulated to ALP branches labelling Cohen as a fellow traveller.

In 1962, Cohen voted against William Haworth's proposal for Australia to raise antisemitism in the Soviet Union at the United Nations.
The government used this to expose divisions between Cohen and the anti-Soviet faction of his party, which included Syd Einfeld, the president of the Executive Council of Australian Jewry.
In reply to prominent anti-communist George Hannan, who detailed instances of antisemitism, Cohen stated that Hannan had exaggerated the problem and that Jews largely enjoyed equal rights in the Soviet Union.
He accused the government of making a "political football out of human suffering".
Cohen's speech was "excoriated in the Australian Jewish Herald" and opposed by the Victorian Jewish Board of Deputies, weakening relations between the Melbourne Jewish community and the ALP.

Cohen was a "vigorous opponent" of Australian involvement in the Vietnam War.
In 1967 he was elected as the deputy to Lionel Murphy, the Leader of the Opposition in the Senate.
He was also elected to Gough Whitlam's shadow ministry, and subsequently appointed by Whitlam as shadow minister for education, science, communications and the arts.
He also served on the council of the Australian National University and the executive of the CSIRO.
His proposals for a Schools Commission and needs-based Commonwealth grants were later implemented by the Whitlam Government.
However, in 1968 Cohen was a member of the ALP Federal Executive that came into conflict with Whitlam, resulting in a leadership spill.
Cohen was elected to the Senate at the 1961 federal election, following a controversial preselection process. His chief opponent was another prominent Jewish barrister Maurice Ashkanasy, who had the support of the Labor Right faction and had opposed the work of the Jewish Council. During the campaign an anonymous pamphlet was circulated to ALP branches labelling Cohen as a fellow traveller.
In 1962, Cohen voted against William Haworth's proposal for Australia to raise antisemitism in the Soviet Union at the United Nations. The government used this to expose divisions between Cohen and the anti-Soviet faction of his party, which included Syd Einfeld, the president of the Executive Council of Australian Jewry. In reply to prominent anti-communist George Hannan, who detailed instances of antisemitism, Cohen stated that Hannan had exaggerated the problem and that Jews largely enjoyed equal rights in the Soviet Union. He accused the government of making a "political football out of human suffering". Cohen's speech was "excoriated in the Australian Jewish Herald" and opposed by the Victorian Jewish Board of Deputies, weakening relations between the Melbourne Jewish community and the ALP.
Cohen was a "vigorous opponent" of Australian involvement in the Vietnam War. In 1967 he was elected as the deputy to Lionel Murphy, the Leader of the Opposition in the Senate. He was also elected to Gough Whitlam's shadow ministry, and subsequently appointed by Whitlam as shadow minister for education, science, communications and the arts. He also served on the council of the Australian National University and the executive of the CSIRO. His proposals for a Schools Commission and needs-based Commonwealth grants were later implemented by the Whitlam Government. However, in 1968 Cohen was a member of the ALP Federal Executive that came into conflict with Whitlam, resulting in a leadership spill.
Sam Cohen (Australian politician)