Schindler, president of Reform Judaism's main congregational governing body --the Union of American Hebrew Congregations -- from 1973 to 1996, died of heart failure at his home in Westport.
With intermarriage growing and Jews becoming more assimilated into American secular life, Schindler developed Reform outreach programs in 1978 to attract assimilated Jews and non-Jews seeking a religious tradition.
Schindler argued that rather than excluding Jews who marry outside their faith, the Jewish community should welcome their spouses into the synagogue and encourage couples to embrace Judaism.
"At the time, to be a convert meant there was a certain stigma attached to you. He said when someone marries a non-Jew, we don't turn our backs on them," said Rabbi Eric Yoffie, current UAHC president.
Schindler also broke with the age-old tradition of considering only the children of Jewish mothers to be Jews. He argued that patrilineal descent should also be recognized, as long as the children are raised as Jews. His stance was later endorsed by the Central Conference of American Rabbis, a national group of Reform rabbis, and has become the standard for many American Jews.
A champion of liberal causes, Schindler also insisted on recognizing the equality of women in Jewish religious life. He was also an outspoken supporter of the rights of gay and lesbian Jews to fully participate in the synagogue, including the right to rabbinical ordination.
Schindler was born in Munich, Germany, on Oct. 4, 1925. He fled the Nazis with his family, arriving in the United States when he was 12. He earned a Purple Heart and Bronze Star for bravery in action as a member of the U.S. Army's Tenth Mountain Division ski troops during World War II.
He graduated from the College of the City of New York before studying for the rabbinate at Hebrew Union College, where he was ordained in 1953.
At the time of his death, he was president of the international Memorial Foundation for Jewish Culture and vice president of the World Jewish Congress, an advocacy group.
Schindler's positions were often opposed by Jews outside the Reform movement, but he remained undaunted, said Rhea Schindler, his wife of 44 years.
"He really bucked the tide, but he always was willing to jump into it, whether it was popular or unpopular," she said.
"He saw it as his task to unite the Jewish community," Yoffie said.
In addition to his wife, Schindler is survived by five children and nine grandchildren.