Scheininger chaired the Canadian Jewish Congress's Ontario region during the 1980s, and argued in favour of public funding of denominational education. He was chosen as president of the Canadian Jewish Congress in April 1989, succeeding Dorothy Reitman. During his acceptance speech, Scheininger said that his primary goal was to improve Canada's relationship with Israel. He argued that Canada's recent upgrade in relations with the Palestine Liberation Organization had " into jeopardy the possibility of Canada providing a useful role in the Middle East process", and said that Israel would have difficulty accepting Canada as an "honest broker" in the future. He said he would promote anti-hate crime laws, and work to mediate disputes between Orthodox, Conservative and Reform communities within Canada. In June 1989, Scheininger criticized the Canadian government for supporting a United Nations motions that condemned Israel's military actions in the West Bank and Gaza. He supported the Israeli government's decision to kidnap Sheik Abdul-Karim Obeid later that same year, and called for Canada to downgrade its relations with the PLO. Unlike some prominent American Jewish groups, the CJC did not openly criticize Israel's response to the First Intifada in this period. Scheininger praised Canadian Prime MinisterBrian Mulroney for his support of the 1991 Gulf War, and described Saddam Hussein's military attacks on Israeli targets as "diabolical". After the war, he criticized External Affairs MinisterJoe Clark for advocating further dialogue with the PLO. Scheininger also called for governments in Canada to prosecute Nazi war criminals and persons who promote hatred toward Jews. He encouraged the Alberta government to initiate a second prosecution against Jim Keegstra in 1991, after Keegstra's first conviction for promoting hatred was quashed. Scheininger stood down as CJC president in 1992, and was replaced by Irving Abella. In the late 1990s, he chaired the CJC's international affairs committee. He was awarded the Samuel Bronfman Medal in 1998.
In late 1991, Scheininger represented suspected prominent Canadian-Croat Anton Kikas in a high-profile case. Kikas was a Canadian citizen, but the Yugoslavian government considered him to be a Yugoslavian national. Scheininger previously worked for the firm of Bresver, Grossman, Scheininger & Davis. In 2006, he provided legal counsel to Liberal leadership candidate Joe Volpe, whom he had nominated eighteen years earlier.
