Klein was drafted as the Liberal candidate in the largely Jewishriding of Cartier when incumbent Liberal MP Leon David Crestohl died suddenly during the 1963 federal election campaign. He served for two terms, in the Parliaments elected in 1963 and 1965. He retired before the 1968 federal election when the riding of Cartier was abolished due to redistribution. During his time in Parliament, he served twice as the Chair of the Standing Committee on Indian Affairs, Human Rights and Citizenship and Immigration. In 1964, Klein introduced a private member's bill which would have been Canada's first hate crimes legislation had it been passed. Bill C-21 proposed the death penalty for anyone who committed murder with genocide in mind and a mandatory 10-year sentence for anyone who, with genocide in mind, caused bodily harm or deliberately inflicted conditions designed to bring about the physical destruction of a group. The bill was intended to "outlaw not only Nazi-type hatred, but all hatred.". However, it died on the order paper when Prime MinisterLester Pearson called the federal election of 1965. In January 1965, the federal government appointed the Special Committee on Hate Propaganda in Canada, chaired by Maxwell Cohen and including Pierre Trudeau The Committee's mandate was to study the issue of hate propaganda and make recommendations on legislation. One of the first things the Committee did was to meet with Members of Parliament who were interested in the issue, including Klein, to co-ordinate the work of the committee and the members of Parliament. In 1966 the Cohen Committee reported in favour of legislation. The Pearson government then introduced a bill to amend the Criminal Code, making it an offence to advocate genocide, similar to Klein's draft bill. The bill also created an offence of publicly inciting hatred in a way likely to induce a breach of the peace, and a third offence, of wilfully promoting hatred. The government bill took four years to wend its way through Parliament, but in 1970, it was passed by the federal government of Pierre Trudeau, now Prime Minister. Klein was also a proponent of bilingualism and French immersion in schools and was an advocate of the new maple leaf flag during the Great Flag Debate.
Death
Klein was admitted to Montreal Jewish General Hospital two weeks before his death. He died there on December 31, 2007 at the age of 97. He was survived by his two daughters.