Leon Harris Charney was born to a Jewish family in Bayonne, New Jersey, to Morris, a sewing supplies salesman who died at a young age when his son was young, and Sara Charney. He grew up poor. He attended Jewish day schools, worked as a counselor at Camp Winsokee, graduated from Yeshiva University in 1960, and from Brooklyn Law School in 1964. He paid for his education in part by singing in synagogues.

He became a member of the bar in 1965, and with $200 in the bank started his own law firm representing Sports and show-business personalities, including Jackie Mason and Sammy Davis Jr.

That effort saw the emigration of 1,000 Jews from the Soviet Union to Israel. Later, United States President Jimmy Carter asked Charney to help advise him during the Camp David Accords. Charney refers to his efforts as using "back door channels", and he advised President Jimmy Carter from 1977-81. In a forward for one of Charney's books, Carter referred to Charney as "the unsung hero of the Camp David Peace Treaty."

The film itself was a source of some controversy in New York political circles. The film deals with the 1979 Peace Treaty between Israel and Egypt and the real-life behind-the scenes drama that led to the historic peace treaty. The film's title is actually an opaque reference to Charney himself, considered by many to be the "back door channel" that enabled the Camp David peace to materialize. In addition to Carter and Charney, the film features former Secretary-General of the U.N. Boutros Boutros-Ghali, Dr. Henry Kissinger, the former U.S. Secretary of State, CNN's Wolf Blitzer, and Senior Adviser to the His Majesty King Mohammed VI of Morocco, André Azoulay and many other international dignitaries who played roles both major and minor in the Israeli-Egyptian peace.

In 1986 Charney went to Tunisia to meet with Yasser Arafat in the hope of a possible peaceful resolution of the Israeli–Palestinian conflict.

In 2003, Charney donated $10 million to NYU Langone Medical Center for a new cardiac wing of the hospital. He is also the major benefactor of the University of Haifa's Leon H. Charney School of Marine Sciences, for which he reportedly donated more than $10 million in 2007.

Charney hosted a national weekly TV talk show Leon Charney Report which deals with local New York politics, foreign affairs and the Middle East, social issues and popular culture. Although his show has been seen weekly on WNYE-TV for years, in recent years it has gained ground since the station became nyctv in 2005, after New York City Mayor Michael Bloomberg took control of the school system and enabled his top media executive Arick Wierson, to merge the stations with the existing nyctv cable channels. Via nyctv, The Charney Report began podcasting its audio version on NPR and began a nationally syndicated the audio component as radio programming.

Charney was the author of four books, his latest being on The Mystery of the kaddish, the Jewish prayer for the dead, which was published in December 2006 by Barricade Books. The book is The Mystery of the Kaddish: Its Profound Influence on Judaism, ISBN 1-56980-300-5 (hardcover), ISBN 1-56980-347-1 (paperback).

In 2008, some thirty years later, Charney, a major real estate owner in New York's Times Square, appeared for the first time on the Forbes 400 list of the wealthiest Americans, debuting at #321. The 2009 list - the first to reflect the world financial crisis, indicated Charney's net worth had fallen in the previous year, although his rank had jumped to #296, up 35 notches, indicating that while he lost wealth, he lost comparatively less than other fellow billionaires. For 2010, Charney ranked #308 on the Forbes 400.

In 2009, Charney was a featured interviewee in a Harry Hunkele documentary film starring former U.S. President Jimmy Carter entitled Back Door Channels: The Price of Peace which is opening in the heart of the Arab world in Abu Dhabi in October 2010 at the Abu Dhabi Film Festival, also known as the Middle East International Film Festival. The film is the source of much buzz in the diplomatic sphere, as it is rumored that many never before revealed aspects of the original peace process were unveiled, some of which paint a less than rosy picture of American diplomatic efforts at the time. It has only been verified that the movie has been shown once, in Monte Carlo, due to a special request made by Albert II, Prince of Monaco, the President of the Festival, to Arick Wierson, the film's executive Producer.

The film has also screened at the 2012 Jerusalem Film Festival and the 2012 Atlanta Jewish Film Festival.