Cherniack was born in Winnipeg, Manitoba, Canada. He was active in the Cooperative Commonwealth Federation and its successor, the New Democratic Party. He was also active in matters relating to the Canadian Jewish Community. At various times he was the school trustee for Winnipeg School Division, Alderman of City of Winnipeg, Councillor of the Metropolitan Corporation of Greater Winnipeg and a member of the Manitoba Legislative Assembly. He is known for his intellectual rigor and integrity.
During his time as MLA, he served as Minister of Finance, Minister of Urban Affairs, and Deputy Premier. In 1970 he was responsible for the first unification in North America of suburbs and inner city into one large city. After his retirement from politics he was Chair of Manitoba Hydro and a member of the Security Intelligence Review Commission overseeing Canada's secret service.