Deiter was a Cree-Saulteaux from the Peepeekisis Reserve. He served as the chief of the Federation of Saskatchewan Indians (FSI) from 1966 to 1969, and was the founding president of the National Indian Brotherhood (1968-70). Deiter was a major figure in the development of Indian lobby groups across Canada, including the Manitoba Indian Brotherhood, the Indian Association of Alberta, the Indian Veterans Association, and the Native Alcohol Council. He also led the fight in 1969 against the federal government's plan to terminate the special status of Indian people and their lands. Deiter's contribution to Aboriginal political development has served as a fulcrum for contemporary organizations and their effectiveness in the granting of collective rights through treaties, as well as their continuing battle toward self-determination within Canadian society. In 1977 Deiter moved back to Peepeekisis and served a term as band councilor; in 1978 he organized Indian veterans to establish lobby groups to pressure for compensation parity. He served as the founding president for the National Indian Veterans Association and as president of the southern region of the Saskatchewan Indian Veterans Association; he also accepted an appointment to the FSI Senate. In 1980, Deiter was honoured as an Officer of the Order of Canada in recognition of his outstanding achievements and services.
Walter Deiter has great historical importance in the political development of the First Nations people of Canada. He was the first Canadian Indian leader to organize successfully national and regional Indian political aspirations into forums that could be understood by mainstream society. His leadership style encouraged unity among First Nations people while establishing a credible presence to the general public. His approach was to confront colonialism in the federal government and to assert the potential of First Nations people to help themselves. He provided leadership at a time when funds for First Nations political movements were non-existent, and his willingness to use his personal funds demonstrated his belief in his people. He was single-minded in his efforts to liberate First Nations peoples, awakening them to new opportunities, empowering them through example, and unifying them towards a goal of self-determination.