A graduate of Yeshiva University, Schneier was rated number 37 of the top 50 most influential American rabbis by Newsweek magazine in 2007, and one of the 50 most prominent Jews in the United States by Forward. An advocate of tolerance and understanding between different ethnicities, he has been honored by the United States Congress as well as the State of Israel, and is the recipient of the Kelly Miller Smith Ecumenical Award from the Southern Christian Leadership Conference, the Martin Luther King, Jr. "Measure of a Man" award from the NAACP, the Ellis Island Medal of Honor, the Civil Rights Leadership Award in Honor of Martin Luther King, Jr., the New York State Martin Luther King, Jr. Medal, and the American Civil Rights Education Services Civil Rights Award.
Schneier is a former vice-president of the World Jewish Congress and past president of the North American Board of Rabbis and the New York Board of Rabbis, as well as serving on the boards and executive committees of numerous organizations. He is the son of Rabbi Arthur Schneier, founder of the Appeal of Conscience Foundation.
Schneier has written and spoken extensively on interfaith relations, and is a frequent guest on television and radio talk shows. He is the author of the book Shared Dreams, an account of the relationship between the Reverend Dr. Martin Luther King, Jr. and the Jewish community during the civil rights era, published in January 2000; the Foundation for Ethnic Understanding, which he founded with Joseph Papp and is chaired by Hip hop mogul Russell Simmons, produced a student guide based on the book which was distributed to thousands of Jewish and black students in hundreds of high schools and colleges in the United States. His latest book, co-authored with Imam Shamsi Ali, Sons of Abraham: A Candid Conversation about the Issues That Divide and Unite Jews and Muslims, was published by Beacon Press/Random House in September 2013.
Rabbi Schneier created and spearheaded the annual Weekend of Twinning’s of Mosques and Synagogues across the globe (2008, 2009, 2010, 2011, 2012, 2013); 1st meeting of the Coordinating Committee of European Muslim and Jewish Leaders in Paris (2011); 1st Gathering of European Muslim and Jewish Leaders in Brussels (2010); 2nd, Gathering of European Muslim and Jewish leaders in Paris, Mission of 28 European Imams and Rabbis to the United States (2009); Mission of European Muslim and Jewish leaders to Washington D.C. (2009) Mission of Latin American Muslim and Jewish leaders to Washington D.C (2012) and the Mission of Muslim and Jewish leaders from the Southern Hemisphere (2013) and the first Summit of Rabbis and Imams in New York (2007). He was appointed to the Steering Committee of the Kingdom of Saudi Arabia’s World Conference on Dialogue, convened by King Abdullah in Madrid (2008) and in Vienna (2009,2010,2012). Rabbi Schneier has also been appointed to the Executive Steering Committee of the Multi-Religious Campaign Against Anti-Muslim Bigotry in the United States (2010). In 2010, Rabbi Schneier served as the keynote speaker at the Doha Conference for Interfaith Dialogue in Doha, Qatar. In 2011, he was the first rabbi to be received in Bahrain, by King Hamad bin Isa Al Khalifa.
Rabbi Schneier has been married six times. For his 50th birthday, his fourth wife, Tobi Rubinstein-Schneier, arranged for a 400 lb. endangered Asian lion to be donated in his honor at the Jerusalem Biblical Zoo. The lion was renamed "Rabbi Marc".
In June 2010, he announced to his congregation that he has been suffering from bi-polar disorder and would seek a divorce from his fourth wife. Ken Sunshine, a spokesman for Schneier, confirmed that the rabbi had been dealing with "a very serious illness," while reaffirming his status as a "renowned worldwide leader, and a pioneer in Muslim-Jewish relations."
The Rabbinical Council of America (RCA) decided in 2010 to investigate Rabbi Schneier for breaching the code of ethics by carrying on an extramarital relationship with Gitty Leiner, a member of his congregation. The RCA executive committee voted to expel Schneier in June 2015. Morris Tuchman, president of the board of Schneier's synagogue, said "We are very proud of Rabbi Schneier’s achievements and are considering no action as a result of this RCA debacle." Schneier married Leiner, a speech pathologist, on October 6, 2013. They were later divorced and Schneier married his sixth wife, Simi Teitelbaum, in March, 2017.