His father worked briefly as a tailor and draper in Griffith, New South Wales, and later as a tyre salesman for Beaurepaires.

He sung in the choir of the St Kilda synagogue, where he became friends with future governor-general Zelman Cowen.

[2] At the bar he specialised in industrial law, where he worked closely with another future Labor MP Clyde Holding, and was a pioneer of common-law workers' compensation claims.

[2] Cohen joined the Australian Labor Party (ALP) in 1946, and served as president of its North Kew branch.

During the campaign an anonymous pamphlet was circulated to ALP branches labelling Cohen as a fellow traveller.

[1] 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.

However, in 1968 Cohen was a member of the ALP Federal Executive that came into conflict with Whitlam, resulting in a leadership spill.